The Ender 3 is a great little system. I've done some very minor upgrades to mine, and it works great. I'm tempted to pick up an Ender 5 next to help speed up multi part prints.
A glass bed and a can of hairspray is the best mod you could do for one.
I did the glass bed. Printing the housings for rpi now. I think the next big mod will be the silent board and bl touch.