You don't float tags against scorch decks anyway or it could open you up to triple scorch... So no problem there.
Even if you have double Plascrete, it's probably wise to not take tags until you think the game is about to end from agenda points, since they can always score the Cleaners. Frankly, unless I know exactly what my opponent is playing, I don't keep tags unless I know I can recover from a closed accounts/mass resource trashing. My money and resources are generally too important to give up like that. Sometimes you AS last click and remove the tags the turn after against Glacier Decks like RP, but leaving your resources vulnerable is how you lose to them in a long game (i.e. most of them).
So yeah, In my opinion, if you have a loose influence, cutting a Plascrete for this is one of the best ways you can spend it. Espessially if you are running Legwork.