Just a personal preference, but the only part I always swap on Glock pistols is I install the trapezoid slide lock from brassstacker.com

Polishing internals is something I will get around to eventually, but they shoot pretty well stock for me. I may dremmel the trigger guard on my 22 and the beaver tail on my 27. If I shoot a lot at one time, without wearing gloves, they do leave red marks on my hands.