Very simular to "Eye of Critical Damage" and magic stones. Sacrifice a pouch slot, To build higher stats. Would be offered in the shop as a permanent item. You could equip as many of each (3 slots max), except for the Enhanced Charms, Limiting you to one. (Hence one +5 and 2 +3 strs could be equipped) Example be like this: 10K Carats = Weak Charm of Speed +1 SPD 200 RC = Charm of Strength +3 Str 400 RC = Enhanced Charm of Armor +5Arm (Only 1 ENHANCED CHARM could be equipped of the same type) HP = 100/200/300 SP = 50/150/250 STR = 1/3/5 ARM = 1/3/5 SPD = 1/3/5 JMP = 1/3/5 CRI = 20/40/80 LUK = 40/80/120 EDIT: It was suggested and I am not particularly against it or for it. Either 1 enchanced only of a certain stat type or simply cant equip the same one twice. (meaning you would have to have one +5 one +3 and one +1 or 3 +5's of different stats possible)
I'd say limit one of each, to prevent even more stacking. So 1 Weak Charm (+1 Stat), 1 Charm (+3 Stat), and 1 Enhanced Charm (+5 Stat) totaling to +9 of a single stat or mixture of 3 stats (1/3/5). If this was implemented, your current suggestion would pretty much enable +11 STR for the price of 800 RC, which is more STR than a +10 STR Gem and 1 STR shy of a full STR Avalon (+12 STR).
9 or even 11 Str is kinda nothing tho today. Plus you would have to strictly focus on STR, give up other possible stats and sacrifice pouch item slots, Which are already very handy. In reality, there is no stat worth more than 2x panic, omni sensor, etc. Also with Avalon, you can gain up to like 3-4 stats with 2 A's 2 B's 2 C's at like +10 each. However sure I agree that 1 each would be fine too. I would like to see someone go all out str/stat mixing and not have a pesky 2x lol Il edit post