If you use an traditional UGF, you need to gravel wash regularly and every 6 months or so, pick up the plate and clean gunk under it. If you use live plants, they will eat the gunk, but get roots tangled in the plate. They are great biological filtration, but gunk can get stuck that slowly decays and makes high nitrates. They also are good for keeping piles of rocks from slipping or breaking the bottom glass if you drop one.
My suggestion would be to try a "reverse undergravel". You should be able to buy a "reversible powerhead" in the 100-300 GPH range for $20-40. Its a little electric water pump that would push the water down the upright tube (put one in the middle and cap the other holes, or get 2 small pumps) that would come up through the plate. In theory, they blow the crud out of the substrate up where the filter can get it. It is hard to get good circulation in a tall tank, so that should help with fewer of the drawbacks of a traditional UGF.