Well, as a Noob in here I might add my 0.02 here.
I'm focussed on the Rolex and associated brands.
I started with 4 cheap reps in around 2002 and went to gens in 2006.
From taste I'm a little aside the mainstream and like "clean dials" as in Ex 1, Oyster No-Date, SubND and if it has to be a chrono, pre-Daytona is the max "dial fuzzing" :lol:
I started the gens with low value ones but soon reached full set 1803 or single watches serviced in Geneva for $2K. Luckily I didn't sell a single gen for less than it's costed me, even if I had transcontinental flights to collect them. So finally I ended up with more than 5 dozen gens and decided that this isn't the way I wanted to store my money. So I started selling some time ago, but as I do it slowly still a lot of them stay with me (or better with my bank deposit box :facepalm

.
I don't know what it brought me to the rep forums but I think it was the idea of building watches from their parts and I stumbled over the possibility to combine my accumulated gen parts with rep parts.
As a kind of watch-tourette victim I couldn't resist immediately buying some reps I liked from members of different forums (already recieved the 2) and different TDs (expecting 2 tomorrow, 2 next week).
For the selection there were relevant:
- my old addiction -> ETA ExI 114270 - sold the gen, bought a rep
- never had a GMT -> got a ETA GMT IIc rep wearing right now
- my daily beater - expecting a asian ETA rep 16600 to replace my gen
- DDs are nice -> asian ETA 218206 with special plain dial to have an understatement dresswatch not to be recognized by many

- vintage Milgauss 6541 -> would have been a gen dream watch, first target to a smooth vintage age modding and also not often seen in the rep forums
- Milgauss 116400BD -> 21j version just to split shipping to more than one watch, never was attracted by the MIG, may be this will be a catch and release or a love for life...
Generally I just will replace the rep crystals with new ones without etched crown where existing as the rep crowns are too large and too easy to spot.
If this doubles the cost of the rep it doesn't matter for me, it enhances the value!
My most expensive rep project is a GMT 1675 in a version I didn't spot in the rep forums until now. I'm still in the parts decision and collection phase, but this might sum up to >$500 for 100% rep finally.
I also will build some DJ frankens as I have a good collection of gen dials and bought some gen cases.
So basically I buy the reps of watches I like to wear.
If they are close to gen it's fine, if not, some details I'll change because they are too obvious for me (etched crown), others are depending on the watch (e.g. bracelet: solid mid links on GMT IIc are ok for cheap every day wear - here I also think to stay with original crystal -, wouldn't accept wrong bracelet details on my special 1675 project).
But collecting reps definitely has to be a thing which is cheaper as collecting gens!
My cheapest gen Rolex is a 1922 9kt gold Ladys Rolex bought with non working movement. Unfortunately while servicing the movement I cracked a jewel so I put it aside for jewel replacement by my watchmaker...
Dee