When you say the foxgloves have "petered out", I'll assume you mean they have stopped flowering. Some foxgloves are biennials and some are short lived perennials. Also, some biennials can actually live for three or more years. If the variety you have is biennial and the plants have set seed fairly heavily, then they probably will die soon. It's hard to predict without knowing what variety you have. If your plants look healthy, just leave them there for now and see what happens. It's too hot right now to plant much in their place anyway.

How big are your maples? Are the branches that are drooping permanent branches or lower than the branches you want to keep when the tree matures? Have you got pictures? Without more information, I can't say for sure what I would do, but right now, I'm leaning more towards leaving them alone and letting the tree do what trees do naturally. It sounds like drop-crotch pruning is not an option anyway since foliage is only present at the tip of each main branch.

Thanks so much for your response. Sorry for my delay - we were travelling and then I had to figure out how to upload a picture. I'v left the foxgloves and I'll just see what happens.

Re: the Trident Maples -- Here are a few pictures. I'm sorry they're not better -- you may have to squint! And there's a small crab apple that partially obscures the view. If these don't work, let me know and I'll try to take some more.
This first one is the worst one.

This shows a similar tree that we put in at the same time, same conditions.

And this is a side-by-side comparison - you can really see the difference between the two here.

Thanks so much for any ideas/thoughts!