Well we all know these potions. And how niche they are. While they are pretty good preps, especially when you know you'll be facing debuffers, but are useless 90% of the time in shops. There are 2 routes that could fix that. First, remove them from shops or sell them with other potions. That's about all I can say about this idea. My personal idea is to give them a universal effect. First change burn salve to spell salve. Then the tonic grants +5 max hp and the salve grants +1 mana. While this is half the effect of a pendant for the same cost, it also retains the poison/weakening or mana burn/corrosion curing properties.
I speak chaos.