I'd plan on replacing it. You need to remove all the undercoating/sealer from the area so you can get a good look. I bet you'll find it's worse than it looks now with all those coatings covering the area up. Could be damage to the surfaces the perch is attached to as well. And while you're at it take a good look at the other side. You might be doing both sides. To do the rivets you need gorilla pop rivets and the proper tool, not ordinary Home Depot stuff. I welded mine.

I went through this with my '96. Somebody had attempted a half-assed patch up repair but that only made things worse. Not a terribly difficult job, and the replacement perches don't cost a lot. I had to patch up the areas under the perches before welding the new ones on. I did it while rebuilding the suspension, so the spindles, control arms, and brake stuff was out of the way for the perch repair. When done I painted everything but did not apply sealer so the area can drain and dry out.

Search the forums. There's more information from other folks who've already been there done that. I found a lot of useful information about the repair on this site and others. Try searching "W210 spring perch" and have fun reading up on it!

Here's a good thread to look through:
http://www.peachparts.com/shopforum/mercedes-parts-reference-library/182420-w210-spring-perch-%3D-front-spring-bracing.html