I think you stated the problem:

"All are somewhat pot-bound."

You can leave mirabilis longiflora outdoors in your climate, if you want. I have one in the ground here in zone 5 which blooms pretty profusely every year.

I know what you mean about potted tropicals not blooming, though, since I have plenty of those too. The one annoying me most at the moment is a two-year-old streptosolen which looks very healthy but has never performed.

I'm not sure the Brugmansia can go in a larger pot. About 20 inches or more now. I need a hand truck to get it to the basement! The others are in fairly large pots too but the profuse vegetative growth requires water every day or they wilt. What about root pruning? Remember Thalassa Cruso?

"What about root pruning?"

Absolutely, speaking generally for container plants, I don't know Brugs well. (They are hardy here though I did try to keep a couple of cuttings in a pot last winter, trying to save about-to-be-frostbitten pieces by making new plants from them.)

Root pruning should be part of almost any repot. Also usually the only way to remove the old soil. And I totally agree, at a certain point, the pot is as big as it's going to get for a certain plant. If roots have run out of room to grow, the whole plant will suffer. Trimming the roots allows space for them to grow anew, and most plants respond with a growth spurt.

Sometimes it's also necessary to prune above the soil a bit to keep things at a manageable size/shape. That would also result in a more bushy appearance, if that would appeal to you. For example, removing the leaves along the main stem/trunk would result in new branches starting to grow where they were.

Could you be seeing stress wilt in the afternoon/evening? Some plants that do not need a drink can wilt at that time of day, yet be perfectly perky and fine the next morning. When these plants are given a drink in the afternoon, it would usually do more harm than good. (Although by the end of a hot afternoon, a severely pot bound plant could definitely be genuinely very dry.) Checking in the mornings can prevent this mistake.

I would be more inclined to believe the plants really do need water that often if the pot is packed with roots. That would mean there's very little 'soil' left to hold moisture for a longer period. If the soil is all or mostly peat, which can become hard as a rock and hydrophobic (unable to accept moisture,) it could be that water isn't penetrating the center of the pot/root ball at all. To find out, water as usual. Ten minutes later, water again. If a lot more water soaks in the 2nd time, you know the soil/pot is hydrophobic. Not good, now the roots have tons of moisture, but no air. Roots need tiny air pockets to stay healthy to obtain oxygen and have somewhere to physically grow into. Needing to water every few days is great from the plants' standpoint, but not if it's because the pot is slam-full of roots. It should be because the soil mix is more chunky, porous, and just doesn't hold excess moisture.

Back to the potted ones kept inside last winter... By the time they went back in the ground, the above-ground parts had died back to the surface, and the pots (about 1 1/2 gallon) were full of roots and at the bottom, they were in a tight strangle of death-spiral/circle. Anytime I've ever unpotted a plant like that, it wasn't doing well and I was checking to see why... These plants had gone from cuttings in October to no more room for roots to grow by April. There wasn't much going on above, but those roots were busy, and took up all of that space that quickly. When put in the ground, (after trimming that "pad" of circled roots from the...