[c0w]

Good question. I'm pretty much the same way. Tons of ideas, tons of awesome projects, limited resources and ability for execution. I think the biggest factors you have to consider when trying to answer this question are viability, difficulty, and ROI.

When evaluating viability you want to ask yourself questions like "Is there really a market for this?", "Would this substantially improve the process of doing X?", "Am I creating a new market here?", "Is this an incremental improvement to an existing product or process or am I adding exponential value?", "Are there companies currently in a position to compete?", "Could an established player in this space do this easily and push me out of the market?", and ultimately: "Would I use this? Regularly?".

Difficulty is fairly obvious and deals with the question of energy in, and whether it's truly feasible for you to pull something like this off in a reasonable timeframe, given your resources at hand.

ROI is the ultimate question that asks "What's the upside?", "Is it really going to be worth my time to solve this problem?", "For the time (money) I invest in building this, is it going to pay out more than the other projects I could have been working on?" (opportunity costs).

Good luck!