Though this subject has been brought up, I would like to see what people consider a good conversion rate... At what rate, do you stop improving your game and lock down the improvements/features?

I am pretty sure there’s no much sense in improvements after reaching 100% conversion rate. So I’d stop after that. Also, 100% is a good conversion rate. :)

Seriously, it depends on the type of your product, its price, your traffic, and your goals. Having 0.5% conversion rate and sell your product for $500 per copy and getting 1000 downloads per day is much better than having 5% conversion rate for 5$ per copy and 100 downloads per day.

I’d suggest to you take the approach once mentioned by Steve P. on this forum. Think about how much you would like to get paid for your project. Say you want $5000 per month. Now the “good conversion rate” will be the rate that will be getting you that amount each month. If you have 1000 downloads per day, and your get $20 per copy sold, than your good conversion rate would be something like 0.83%.
Once you reach your goal you can stop tweaking your product.

See, conversion rate is not the only factor to consider.