Here's the deal. I'm a pretty reasonable weight (160-165 lb at 6'), so I'm not primarily interested in either slimming down or bulking up. (I wouldn't mind losing a little fat, I'm actually sort of anti-interested in bulking up even if its muscle -- I rock climb and heavier me means more weight to pull up the wall.

However, you know how people describe those who are really in shape as having the aerobic capacity of a horse? Well, I have the aerobic capacity of... whatever a not-horse is. I'd like to improve that.
I've gone a few times, mostly doing intervals. So far, I've been doing 30 sec. work periods and 1:30 or 2 minute recovery periods, with 4 work periods in a trip to the track. (I run at an indoor track, though I've thought about doing a stationary bike too.) My work periods are going near all-out, and my recovery periods are at a fast walk. (That's probably ~12-13 mph work, at least for the first couple, and down to ~3 mph recovery.) My hrm watch is kind of obnoxious to use so these numbers aren't perfect, but I usually end the work period with a heart rate of around 175-180 bpm and start back up around 150 bpm. Finally, I notice myself going noticeably slower in the 4th interval than the 1st and second, and my heart rate seems to drop noticeably slower in the later rest periods. I'm also pretty darn happy when my watch finally beeps on the last work period.

So here are my questions:
1. Is interval training a good way to work towards my goal, or should I be doing something else?
2. Am I making the difference between work & recovery too extreme (and should back off on the work periods so I can go faster during recovery)? (This site seems to suggest so.)
3. As I improve, what balance should I strike between adding more intervals and decreasing the rest periods?
Edit: Oh yeah, right now I'm doing this twice a week, Mon and Wed. My general schedule has me doing that on Mon and Wed, some climbing some Tuesdays but primarily Saturday (and some Sundays). My climbing is primarily anaerobic; it doesn't get my heart rate or breathing up too much at all. I also juggle Thurs and Sun., which is actually a low-level exercise.