A good cleaning should help those records. If you don't want to invest in a cleaning machine (very pricey), you can DIY for about $5 in materials.
Mix a drop or two of liquid dish soap (no more) in a bowl of distilled water, but don't suds it. Warm that in a microwave for about 10 seconds. Using a micro fiber cloth, clean both sides of the record being careful not to get the label too wet. Dry with a second micro fiber cloth. Stand in a dish rack for several hours to fully dry. I bought a 10 pack of towels at Target in the auto care section, and they work great. Don't use tap water because the calcium will leave water spots. Get them good and clean and they should stay clean for some time if cared for. A good cleaning is probably the best way to improve their sound.
This stuff is great for reducing surface noise and improving the sound:
Gruv Glide 800-229-0644 Gruv Glide
This is supposed to be the best affordable brush (used before each play):
Audioquest Carbon Fiber Record Brush 800-229-0644 Audioquest Carbon Fiber Brush
To clean the stylus, stay away from the liquid cleaners as they can wick up the stylus and into the cartridge. Get a Magic Eraser, cut off a small piece, place it under the stylus on the platter, and then lift and lower the stylus into it several times.
I rediscovered my records from the 70s and 80s after my wife gave me a record player last year for Christmas. Good times!