I'm reading a lot on these pages about people quite freely mixing different practices from different traditions together and considering the results quite favourable.  Whereas, in the wider world of spiritual mumbojumbo I hear a lot of "don't mix your drinks" type warnings.

A question I'd love to get your thoughts on:               
Is everything compatible with everything else?  Have any of you discovered any two practices/techniques/etc that just don't go together and can cause problems if you mix them?

First a couple of my own thoughts on this question...

I'm doing a fairly mad old mix myself.
Self enquiry stuff, yogasana (vinyasa style), temple style tai chi I've been learning from a master in guatemala and what started off as goenke-style vipassana, now gone a bit mixy-matchy after being influenced by MCTB and all you liberalists non-traditionalists on here ;) and play with other bodywork, surrender yoga, experimenting with trance states, ecstatic dance type stuff...yeah, I wanna play
Results: All seems fine so far with this mad mix, my brain hasn't completely exploded, but I can't compare to how much more or less progress I might make if I doggedly stuck to one or the other.

Some may say its all fine but less direct and will take longer to reach the big goals, like taking a windier journey to the destination, taking in more scenery along the way.  Goenke makes an analogy of drilling holes for water - much more efficient if you pick a place, drill down, trust in it  and don't shift to a new location even when it's just rock, and eventually you hit the jackpot.
but I'm still not totally sure about this.  
could we not say that:
Concentration is concentration is concentration.  Regardless of the object.
Insight is insight is insight. Regardless of the object.  
??

Clearly it takes a lot of time in my day to do all this stuff, but that's something I know I have and if I only had my sitting practice then I don't know if I'd have the stamina to do 5or6or7 hours sitting every day, self directed.  But mixing it up with standing and asana - it's easy and enjoyable and my retreat-like days have a pretty rich timetable. 

I also think of a yoga teacher I met in Guatemala who warned me about doing too much "spiritual shopping", suggesting to find a teacher and a tradition and go for it.
But afterwards, thinking back it occured to me; the yoga tradition that she chose and went for includes self-enquiry,asana,energy work, pranayama, bhakti yoga, mantra, sexual practices, all kinds of different sitting practices such as focussing on the spiritual heart centre (which i'm guessing could work either concentration or insight or both depending on person-to-person subtleties of how one does this)
So she's still got a wild array of fun things to choose from. the only difference is all this tantalising catalogue of techniques which probably developed all over india and different places at different times just got neatly grouped into one system thanks to good communication and sharing of knowledge and techniques   i.e. the same thing that's now going on with this forum !  (?)  (perhaps if the communication lines back in the day had been stronger from china to india, the yogis would've called Qi Gong a form of yoga and it maybe grouped as pranayama)

Incidentally, I noticed only aftering reading MCTB that I'd been doing tai chi with a strong insight/self enquiry bent.
That is, rather than simply flowing the energy, I was (partially without realising I was doing it, having done a lot of self-enquiry work) enquiring into "Who is moving the energy?" and then after doing Goenke's 10day dance: "What is the raw sensate experience of the energy?"
And the results I experienced from this map neatly enough onto the insight stages.
So then I decided to 'ignore the three characteristics' of whatever was going on to do it purely as a concentration practice and the results were very different. The movement flowed a lot more smoothly and the energy and energy centers filled a lot more of my awareness and became a lot more 'real'.  
So this could be seen as either a case of my alternative experience messing up the intended tai chi experience (?maybe), or of how different techniques can add perspective and dimension and freedom to one another. and eventually all be seen as the one ultimate truth that they are.

Also worth noting is that I purposefully chose a very physical-body oriented yoga practice to compliment my subtle-energy body oriented tai chi practice, just in case two separate energetic disciplines might be working against each other or cause issues - any thoughts on this?
Then with the insight stuff in there there's a good 'integral' balance of gross,subtle and causal.  (and all that integrating can get so controlled and tiresome that you've gotta finish off each day with a good bout of disintegration! ;) )

Ok, so my own thoughts are quite sprawling here, but maybe something in it will help spark something in you. I refer you back to the original question

I think the biggest thing is just consistency and longevity with any practice, regardless of how many you're doing.

I studied some serious "surrender yoga" with a great teacher named Stuart Perrin, who also used the oil drilling metaphor.  It always stuck with me.

The second thought I have is to use your meditative intuition, which you obviously have based on your tai chi descriptions.  What feels right at a given time?  What are the recurring patterns with what feels right as you mix these techniques, week after week?  I've been able to skim the fat from my practice, doing only first-gear noting with mental labelling in daily life, either with sense-object ("seeing computer") or only sense ("seeing").  

uh-huh. yep.

i often feel like meditation is like art and a specific technique is like a composition.
you can play someone else's song or write your own.  
you can also learn multiple styles to have more juice to add into your free improvs.