My inclination with bikes is to just ride them as they are, so long as they are roadworthy when acquired. I'll swap tyres around, and replace consumables, but that's pretty much it unless I am talking about a hack bike put together from skip salvaged parts.
The danger is by incessantly messing around and swapping things, you don't necessarily end up with a better bike, but it ends up being a costly process. All the relatively low-value purchases can soon add up to more than the cost of the whole bike, and you will never get this back if you resell it. Tinkering can be interesting to do, but it really needs to be done with a clear purpose and intended result in mind.