I'd recommend the aeropress over the mokka. But I think to really get into lighter roasts a cheap v60 is the way to go.
You probably won't lose your love of medium roasts but you likely will find some cool new coffees that you will enjoy in a different way. There is so much variety in the lighter side of the spectrum. I think it's completely unfair to make a blanket statement about not liking lighter roasts. Especially will all the coferments and crazy stuff going on with lighter roasts, they really don't fit at all into a simple flavor profile category.

I find them much harder to perfect the brew though. It's also much more rewarding when you finally nail it.

As a suggestion, if you are interested in exploring I'd recommend starting to do this with a good local roaster /barista. Tasting a few well - brewed cups in cafe will give you some framework at least of what the light side has to offer. Personally when I started brewing my own light roasts I made so many lousy cups I never would have stuck with it if I didn't already know that there was a real prize for getting it right.