Over 30 second loops are very easily done without coming close to the filesize limit.
I even have
a song that is 2:16.4 in length, yet only takes up 837kb of space.If you use audacity and export as .ogg, click on Options.

and set quality to zero

As far as I'm concerned, there is no incredibly audible difference. I've found that very rarely, higher tones can sound slightly hollow, but the quality difference isn't all that noticable in game, unless you're wearing studio headphones or something.
I've hooked up Hooked on Feeling for the first little bit as a sample:
Quality 10 - 2.28MB (Stereo)Quality 0 - 385KB (Stereo)As said, I can't really hear a difference between the two, and if there is a difference, it's heavily negated by the savings in filesize.
Audacity has the quality set to 5 by default also.
Point is: 30 second or longer loops shouldn't really be a question that needs to be answered unless you have an automated system that swaps out songs on a predetermined timeline.
I find that the length loops can get when the quality metre is set so low is very helpful with songs that are difficult to find loops for in a certain time frame. It gives much more room for exploration in finding the perfect loop.
However, I am not endorsing posting full songs. Don't do this, filesizes should be kept as small as possible, and this is something that helps greatly.