I purchased a DE Star Trek a couple of weeks ago. It was dingy and neglected, buy not abused. I fixed a number of burned connectors (GI!), replaced locked transistors in the lamp matrix and scrubbed it up. I also removed the 27 ohm cement resistors in the lamp matrix on the MPU and swapped the TIP42s for MOSFETs (Very simple. Pinwiki shows how).
I just completed a shop-out that included LEDs and flame-polishing of the ramps. It turned out better than I would have expected. Next will be installation of coax speakers in the head and an 8 inch sub in the cabinet. I have done sound upgrades to several DEs with stereo sound. It is simple, cheap and the results are outstanding. Here's a link to my BF sound upgrade:
https://pinside.com/pinball/forum/topic/suppose-we-flipbatman-forever-club/page/10#post-3505929