I am totally agreed with By-tor but i would like to add some of my personal opion:
For me a rep is always a rep no matter how much mods and money spent on it. At the later time down
the road and maybe you are no longer thinking highly of it anymore due to your changes of style and thinking.
At that point you want to be able to sell it at good price or get as much money back as posible your invested money.
So Who did the modding is also important in my opion.
Anyone who has enought tools can mod a watch but the end result differed from one modder to the other and the nicer the mods done to it the better resale value the rep is. I have never puchased one modded rep before and i don't think i will later neither. I don't belive in spending over $500 or more on modding the watch and when buying rep, i am looking at the rep to gen cost ratio and i am staying below 10%. Rigth now i am only buying replica watches that i think i would never be able to afford or never to pay for the retail price. If a replica costs about 1/5 of the used gen, then i buy gen instead but i am willing to wait longer. Therefore, my collection up to now only have a few (1 super SD as my daily beater, 1 rolex daydate, 1 rolex daytona, 2 HBB and 1 Dewitt is comming) and i rotate my rep very often. I have 2 gen (1 gmt master II and 1 po 42mm) and i don't wear them often anymore.
Well that is my 2 cents.