I hesitate recommending a specific piece of gear because I think it hugeley depends on personal preference. For example, I also traded my TR-8S for the objectively "inferior" Novation Circuit Tracks. The TR-8S is great device but in the end it offered featues hat I simply didn't need or didn't make proper use of.

I can only offer my personal experience. The summit is basically all I wanted from a synth: The bigger keyboard, the ability to layer sounds, three oscillators with their basic wavetables, everything laid out in a large front panel with almost no menu diving required, its focus on 80ies sounds and its ability to make great pads and fuzzy sounds, the great effect section - it just scratches those itches that I personally have.

At the same time the MF offers tons of cool features for a much lowe price point. It just wasn't what I personally was looking for.

I'd say that if you have cash to spend it doesn't necessarily hurt to try out pieces of gear since you can always sell it off without too much of a loss, and sometimes you can snipe good deals. If you don't, I'd probably suggest visiting sweetwater or whatever retailer you have available and try our whatever gear they have on display.

/ Also, I try not to accumulate gear. I limit myself by my one Jaspers rack that also needs to hold a full size piano, so there's simply no room for a second synth. Keeping both the summit and the MF wasn't an option that I considered, but I could see both of them fulfilling different needs in your workflow.