Cheap, cost effective, and flexible is a Disting. The various implementations of the Radio Music / sample playback & scrubbing means you can take looong files and add them in the background for texture. Field recordings? Breakbeats? Whale songs? It’s all there to be modular-ised. It can also be roughly 1,400 other things in a pinch.
You have random covered with your Marbles clone.
Having flexible / related modulation is useful, for that either the Just Friends that someone mentioned or a Tides 2018 gives you lots of options. I could consider keeping Maths just for its flexibility and use as an envelope follower. The trick is to find ways to mix / combine control voltage to find unpredictable results.
For oscillators, the world is your oyster. I’m partial analog menu-less stuff, but something like Plaits gives you a lot of timbre options.