TL;DR
Allow a user to directly create a parameter signal as a filter, or as a signal in a combinator.

What?
Inserters with parameters as filters can be created, but only by placing down a generic blueprint (see the image below). The same goes for recipes, signals, train stop names, etc.

I'd ...

I love the new "increase quality" and "decrease quality" shortcuts, and I think it could be applied to upgrades / downgrades as well.

Alt + scroll changes the quality, so how about control + scroll to change the tier. This would apply the "default upgrade" upgrade planner to the current item you're ...