Well, different brands of fans have different CFM ratings and db ratings. There are sleeve bearing and ball bearing. Depends who you talk to what is better. I've had both last a long time and fail, so I buy what's on sale. But at 200 fans, you're probably looking at $200 or so, give or take 10-12%.
SOMETIMES the fan state their CFM, but not always, so you might want to call tech support on this one. You might also need to change to the correct terminations, which may or may not be cheap. It won't be super costly, that's for sure.
As far as cooling issues/heat issues, that could be a problem. You might want to find some heat insulating wrap designed for electronics and wrap it around the fan wires, which will help. I can't see that costing much.
Most fans are configured to blow hot air OUT, or rather pull air through the fixture, across the item needing cooling, and the back out. That's what most computers do. I over-fan, so I have a filter on the front, and fans pulling air IN, and then additional fans pulling hot air OUT through the back, top and bottom.
You don't want to blow air in, as that will deifnately pull in way too much dust, and a cool blast could cause the glass on the bulb to shatter and there goes another bulb!
YOu also want to ensure the fans that come with the fixtures and youre replacements are of the same power rating, but at 12v DC, I think you're not going to have problems finding matches. Check your clearances though!
ADJ does sell long life bulbs for these fixtures, but at $25 each, well, can you say "ouch" for 20 of them? That's a $500 pop right there for a fresh set.
Also, since we're talking airflow, where are these mounted? Is this a mobile application or a club application? Maybe you need more clearance around the fixtures. Maybe if it's a fixed location, adding some small fans or a large fan to move the air around might help? Mabye a set of strategically placed ceiling fans?