Just use a metal file to sharpen your plexiglass scrapers. Edges just get rounded is all, square em up. No reason to buy new ones... actually if you know of a sign shop near you, you can prob get some acrylic offcuts for nothing and use those.
As for metal scrapers, i've been using one and as long as you are careful not to gouge into your base then you should be good. Even saw a 'pro' at the shop doing it. Must be legit