I've got the 30 led RGB around the ceiling in my theater and just finished a few weeks ago running them all along the eaves of the front of my house as supplemental xmas lights. I can try and get some pics of the outdoor ones if you're interested.
Anyway, the 30 vs. 60 will depend on what you're using the lights in your theater for. For ambient light or accent lighting, the 30 strips will be perfect. I've got mine set to go to the dimmest red setting possible during the movie, like the perimeter lighting at the theater. The 60 strip for my application would probably be too bright and distracting. Using them as direct (or indirect in this case) primary lighting, the 60 strips would probably be preferable. I put some into a crown moulding to try and sell the wife on the idea of using the strips in moulding like you're planning. The 30 RGB strip put out a nice colored accent light, but definately would need to be supplemented with additional lighting. I put some white 60 strips in there and they were plenty bright as indirect lighting, but my opinion was that I'd need to add some additional lighting. For the living room, I was thinking if I did the crown moulding with led strips that I'd use wall sconces or recessed light cans to add to the indirect lighting. For a theater, I think the 60 strips would provide the perfect diffuse, indirect effect when coming from behind crown moulding.
For outside, the 30 strips seem plenty bright and have a spacing that blends well with traditional xmas light strings. The 60 strips would obviously have a higher density. At night, the 30 strips seem more than adequate for xmas decoration.
I can't speak to their use in a pool, but with my experience, I'd think if you do the entire perimeter of the pool with them, the 30 strips would provide enough light.