I know that interfering with a pre-warp culture is a violation of the Prime Directive, nevertheless it would be interesting to visit pre-warp world. For instance, wen you are exploring an unknown system you could encounter a pre-warp civilization and in order to explore it you could beam down to the surface using a disguise and studying that singularities off that culture. Also there could be mission that would require you to stop a faction (Klingons, Romulans and others) of interfering in a pre-warp culture.
On many of the daily explore missions it will say "There is a pre-warp culture not but 500 km's away, we need to be quick and covert" but you never actually see any signs on life, which always annoyed me, it would be great if you had to encounter those cultures and either stay hidden or with a disguise or something else even.
Cloaking generators break down at first sign of language.
A duck blind mission observing pre-warp cultures could be quite fun, especially if you and your away team were issued isolation suits so that you could sneak up and observe the natives without raising a ruckus.