I have no reason to think you keep the materia because the i230 and i240 simply aren't the same item in the database.

Also, I have big problems in seeing why I should spend, just for the accessories, about 4 millions total in Strength Vs when I can spend 60k for IVs and have a mere 18 AP difference or so, out of 850+.

If some people want to call me "gimp" or whatever, all the more power for them but I'd invest that gil into power-leveling my crafts instead. That's just me though.