The key obviously is to avoid succumbing to upgradeitis, and to make the most of what you have.
I bought my Mojo HD back in 2010, when I was offered the frame at a good price to replace my existing Mojo. Couldn't really turn down the opportunity, the old frame (well 6 months old ) was a bit outdated.
Moved most of the old stuff across, and really only replaced broken stuff ever since.
Oh, except for wanting to try it in 160 mode, so bought an RC4 and limbo chips, and some Lyriks to beef up the front end. Old Arches had to go as well to suit the gnarr mode, so put some Flows on. And the Joplin was pretty unreliable, so rather than continually getting it fixed it was sensible to replace it with a Reverb. Wider bars and shorter stem helped with the handling as well. I think that's what I was told, anyway. Melted a brake hose on the old frankenbrakes just as CRC had a big discount on Saint brakes, so that was handy. Stripped a pedal thread on the cranks, so thought it would be a good idea to swap to a clutch mech and 10 speed at the same time- wasn't sure about the reliability of a helicoil in the pedal threads.
To be honest, I have bought a couple of things that weren't strictly necessary though- CK bottom bracket, Narrow/Wide chainring, but in the main its the same as when I bought it all those years back. Ridden it all over the world, thousands of miles, with nothing more than a few changes of tyre to suit conditions. Every now and again I get tempted to upgrade - direct mount mechs, 650b compatible swing arms and so on, but after sleeping on it the urge goes away, and I can always use the same money to just buy another bike anyway.
Oh, and top tip: if the manufacturer expects you to replace the linkage bearings by buying a new set of rockers , then don't- buy some decent tools, and some bearings, and do it yourself. I wish I'd known that at the start. Save your money for a rainy day.
PS Cane Creek Headset. Still on the original bearings. Only part left from the original build.