Subarus are notorious for heat shields loosening up and/or falling off. I don't know what was done for $65 - but once these things loosen up, their end is not far away. I see heat shields lying on the road every day - probably many from subarus. What the shop told you is correct.
I would decide on a replacement depending on cost. Personally, I'd leave them off if replacement cost more than about 100 - but then I'd have to be careful about not parking over any dry grass. Of course, for the sake of liability, I can't recommend what you should do.
I have used the rattling heat shields as a bargaining chip when I bought a couple of used Subarus. The loose heat shields made the cars sound awful and so, I was able to negotiate a much lower purchase price, then I just crawled underneath and put on some large hose clamps until they fell apart.