Sliding unsleeved records against each other in storage or handling is not a good idea. Damages the playing surfaces. That's why you don't want to leave the records uncovered. As for value, it depends on what's on the record, and how much people want it.
Over the years I have often come into records that didn't have covers. It's not uncommon, but you really need to get them in sleeves for protection. If you toss the record for being unplayable, you can always keep the sleeve.
You can buy the paper sleeves for records from Bags Unlimited for dirt cheap. I'd suggest that you at least put the record in a paper sleeve for protection. Makes it easier to handle, too. You don't touch the playing surfaces of the record, you handle it by the edges. Bags Unlimited also sells plain white cardboard sleeves for records. I keep these around for when I get a record, 78, 45 or LP that doesn't have a sleeve. www.bagsunlimited.com
. How many records do you have? Might be worth it to buy at least some paper sleeves and cover them up to prevent further deterioration.
If you want to sell them, they will sell easier if they are in sleeves. Look less like they have been rode hard and put away wet. Also helps people to look at them.
Hope this helps!
Good luck from that baggy old guy with sleeves.