How much to upgrade ??

[MMarchant]

Until when does it make sense to upgrade a cheap bike ¿? 

I have a Trek Mamba 2012 as my beloved "cheap" (increasingly not so) bike. 

I have upgraded:
- Brakes to Shimano XT 
- Pedals to Crank Brothers Double Shot  (Learning to ride Clipless)
- New and same 3*9 Shimano Alivio it had before (Renewed after 5 years)
- KS ETEN R Dropper 27.2 100MM  (will arrive soon)
- Tubeless Continental XKing 2.2 
- Sunrace 9 Speed 11-40T Cassette  (will arrive soon)

... and now 'm looking to buy a Rockshox Recon SoloAir with a Straight Tube and quick release.

There's two options with that fork, one with 46MM offset and another with 51MM (which is the same as the original Rockshox XC 32 TK ) after reading a few blogs i've concluded to better not mess with the offset to keep the G2 Geometry intact.  

So here comes the open question... 

Should i buy the fork as the crown jewel of my remastered Mamba ¿?  or just stop the overspending and focus on getting a better bike ¿?  

When does it stop to make sense to keep upgrading an entry level Mountain bike ¿? 

 

A bit about me:

I live in Chile which has a lot of mountains ( That's why i'm excited with the 40T Cassette, and i've purchased the XT brakes after some severe finger cramps while descending).

I've dirt biked for years and started mountain biking more seriously a few moths ago.  

I use my bike for XC, Trail, Asphalt, and TACX Galaxia Rollers to improve my fitness for a race in about 6 months.  

I'm also saving for a Trail bike, FUEL EX 9.8 to get a little more comfortable on the harder Trails, The Enduro bike Slash also winks at me every time i see it... but my riding buddies are more biased towards XC )

I'm a Trek Fan and have a decent deal with them as i work with the distributor here in Chile, that explains the Trek fixation.