Would you?
 

Here is the delimma I have:
I got an old classic gun in my arsenal, TM MP5 gen1, I was planning to put a titan in it but now I feel conflicted. Would doing so lower the value(not monetary value, but authenticity value) of the gun?

If I do so the only part that is replaced is the trigger part, but the gun would be considered an upgraded gun. (like putting a android auto unit, in a 1980 BMW)

Depends, are you a collector? do you know someone who is a collector and will smack you? Do you plan on selling it? If you want to game it and dont plan on selling it go for it.

my long term plan is to game it once in a while, twice or three times a year max. I know down the road I want to keep it on my wall as a reminder of history or give it away all depends on the circumstances i will be in.

I did not have a good experience with the Gate TITAN I installed. It is coming back to me to be replaced with a Spectre.

Is it a virgin gun, aka never been taken apart. IF so leave it the hell alone!! TM's operate best when not fucked with.

This is a simple issue. If you're going to run it anyways, then go ahead and upgrade it, just keep all of the original parts in a box somewhere (unmodified). If overall you're worried about its intrinsic value, then don't game the gun, nullifying the need to upgrade it.

It's a matter of economics.

Does the gun matter more to you as a collector's piece or as a workhorse?

If it's more valuable with 1980's TM Pixie Dust, leave it be.

If it's more valuable fragging noobs, start upgrading it.

The choice is up to you.

It being a collector's piece means more to me. With the looks of it, I will leave not do the upgrade. I like to have a historic piece.

Good choice. Cyma MP5s are available cheap and by the crate full, just waiting to be fallen on and snapped in half.