Thank you for being such a good steward of a lovely community resource! The LFL near my house occasionally suffers from the ailments you mentioned — jumble, books that have stagnated there for months — but nonetheless it is a delightful stop every day when we walk the dog. I love seeing what's new in, snagging interesting-looking reads, and I also love contributing from my personal library. I do try to rearrange the inventory when it's looking a mess, but the idea of swapping out chunks with other nearby LFLs hadn't occurred to me.
Pointers: If you're going to build one of these, don't make them too deep! A foot deep is actually sufficient, I think. Not more than 14 inches. Multiple levels are great. My favorite mini library has 4 levels: a pretty tall bottom level -- some books are tall! -- and then gradually shorter as you get to the top one which you can fit paperbacks into. Also, quantity: It's nice to have a little free space so people feel they can leave books. You can put one or more books facing forward so the full front cover is viewable. This also makes the library more attractive. Too many books is not good. Then it's hard move them around to find things. Also, a jumble is no good, I like to keep it pretty well arranged. If there are extra books, I just bring them inside for my next bike trip.
Have fun!