Ah, this brings back memories of my senior year at UW-Madison. Senior design. I'll add my $0.02.

1) Do you currently own or are planning to buy a roof rack?
-Don't currently own, possibly buy in near future.
2) Would fold down side rails be a feature you would find useful?
-Only if I could climb on them to access the top easier. (Standing on the tops of my rear tires is NOT always fun.) Else it just sounds like more bulk.
3) Would a sliding or resizable basket be a feature you would find useful?
-Again, if it eases access to the top, especially when hefting big heavy bulky items, then yes. Else light weight would be better.
4) Would a spare tire mount on the rack be a feature you would find useful?
-Nope, again, back to luggin bulky items around and overhead.
5) Please list some of the must have features a roof rack would need to incorporate before you would consider buying it.
-Aerodynamics
-Light weight
-Quick attach/removal
-Adjustable
-Decent price of course!
6) How much would you be willing to pay for a rack with the criteria you listed above?
-$250 to $500