Speaker Repairs
The most common repair needed, by far, is replacement of the foam surround on the woofer. Many folks refer to this as 'woofer rot', which sounds gross, but is actually a good description. I'm not going to go into detail on this repair, since a number of folks have already done a good job. For the DIY'er, you can buy the parts at Winston Electronics (my favorite) or Simply Speakers, and complete the job yourself. Cost will be ~ $30. I always buy the 'deluxe' kits, which includes a pair of new dust caps and alignment shims. The shims help align the voice coil in the magnet assembly, and prevent future problems. Alternatively, you can remove the woofers and send them to Winston Electronics. Cost will be about double.
I've had to refinish a few Walnut veneers. It's amazing how badly some folks treat their speakers. Formby makes a good 'face lift' kit, for cleaning, restoring and refinishing wood. Be careful - that walnut veneer is only 1/32" thick!