If there is a connector, AND you are going to use the external keyboard a lot, then it would be ok to break out the cover I guess. Then again, why would it be there covering a useful connector?
If there is no connector but you've got the skills to solder one (and everything that may be needed to get it to work), it's just a great little adventure to get it to work 😀
If this ones is already modified a lot (ram upgrade, CF/SSD, hotel), it may be ok, since it's already been tugged into the 21st century.
If you're not going to use the the laptop much, or at least the external connector, and the existing keyboard works fine... I'd skip it. That would keep its original condition (and value).
On the other hand I don't think it would lose much value on this... It's not like you're going to put a Ryzen and 2080 in that would not be worth a single penny in 10 years from now 😉
Looking at my IBM model 30 systems: one is mint, even with all the ISA slots having their plastic caps (also breakable) and another has them removed, to add VGA and play around with other cards. No regrets as it's just a machine for fun.