Many of us start off with a lower quality bike and we have 2 choices. Wait until we can afford a better bike or upgrade the initial purchase until it gives us a respectable ride. I do not have the finances to buy a top grade bike, so took the cheaper way out of buying a reasonable bike and gradually upgrading it to give me a bike that suits my body, suits my riding style, and gives me a bike that works.
Forget about my Tandem as that is the reason I have a money shortage, and not many of us will be prepared to spend the amount I did on that thing to purchase, then more money to upgrade and even more money to keep it running. On my solo however, 5 years ago I bought a Bianchi Hardtail mountain bike with an excellent frame, but bits attached to it that I knew were going to need upgrading very soon. All I have left now of the original bike is the frame, front mech and bar stem. Everything else has been replaced with higher grade parts as the originals failed.
Drivetrain has been upgraded to XT except for the original cheap nasty Acera front mech that still works and does its job perfectly. Brakes are still V Brakes but LX quality as These work as I want them to. Bars were changed to riser bars, and the saddle, after a few comfort problems has been put back to my long favourite of a Flite Titanium but the new version with a little gel and the cutaway. Wheels however did surprise me in that the Original Bianchi wheels were Good. Admittedly they are now the 3rd spare pair of wheels, but are still servicable.
Barring the Rockefellars out there- What are the upgrades that you would recommend to newbies to get their bike working to its maximum, before they decide to sell the wife to get their ultimate bike?
(Edit) Sorry about the sexist bit of selling the wife, but What would you part with to get your ultimate bike.