I guess it sounds like you recommend just doing whatever comes up and what I feel like at the particular sitting.
Well, its up to you to find out what works best. This may mean experimenting with a single technique for a long period of time (ie. observing the rising/falling of abdomen and other sensations coming up). Eventually you should get a feel for what you are missing, whats not being observed, whats causing problems,... and concentrate on those (meditation becomes more experimental and personal with time).
Wonderful book that explained noting for me and gave me a technique to follow: http://books.google.com/books?id=YnedD2Jj3IIC&printsec=frontcover&dq=the+progress+of+insight#v=onepage&q&f=false
I guess I feel that if I am constantly wandering around it seems to interfere with one-pointedness of the mind and samadhi. However if I stay on one spot and dwell there it seems to foster a sense of samadhi. Or is that not the goal with the Mahasi technique?
Okay, reading MCTB by Daniel Ingram may explain this matter (far better than I know how to). Concentration practice leads to non-ordinary states, insight leads to liberating insight (ie. stages of insight, paths, arahatship). In any form of insight (not just noting) solidity (as produced by the practice of concentration) is a problem, it is a sign that that particular phenomenon is not perceived clearly enough, as all sensations are impermanent and constantly arising and vanishing - if it appears solid, it needs to be broken up by noticing the impermanent sensations that make it up. So no, producing stable concentration states is not the goal of insight, quite the opposite.
What is needed is to keep your attention on the sensations that make up your present moment experience (to the best of your ability at that time, which will vary), for which noting is very helpful. Nothing more. The two books I mentioned are great for explaining this in great detail.
I realize that we are not doing samatha but rather insight practice but I guess I feel that some element of samadhi is needed for insight practice as well. Is that true?
Well, concentration is needed in order for your insight practice to be powerful enough to take you through the stages. But this concentration is also produced (strengthened) by the practice of insight, ie. if you note you will improve your concentration anyway. There is some controversy over doing insight only as opposed to doing samatha first in order to build up on concentration before attempting insight. It has been my experience that insight only is good enough. So yes, you need concentration (but actually not so much of it) in order to get a path (if that is your goal) but the correct use of an insight technique (noting) will do the trick to get you there.
Is this at all helpful?
All the best in your practice.