When I need a new laptop, I'll get one. Until then they should not touch!
Almost right - I fix em for a living too... When I shop laptops for myself or my clients, I am looking for bang-for-buck... Usually worrying about processor more than any other thing... then over time, jack it up with a hdd, more ram... Also it is generally true that a laptop can benefit from a wireless card swap, once in it's life...
The one I am on now is about at it's usable end - It was cheap in it's day - around $450 on black friday sale... since then it has gone through 2 hdd replacements - the first to give me more room over the small one it came with, the second to convert it to SSD... It has had two replacement wireless NICs - one replaced the damaged original 'N', the second to upgrade to ac. And I have jacked the ram to it's ceiling. It's also been disassembled twice, down to the CPU cooler for a blow-out, and had numerous replacement keyboards (I am THE keyboard murderer of all time), and maybe a glidepad or two.
That sounds like a lot of service, but really, with the exception of the tear-downs to blow it out, the rest is easy access through panels or removal of a piece or two...
As a rule, I can service a laptop just as easily as a desktop - hardware R&R is doable to a point. It is rare to do major surgery on one, just simply because the numbers don't add up - replacing a MB is exceedingly rare - the cost of the part, plus all the time necessary to put it in will usually exceed the value of the machine. However, on a top-flight laptop, sometimes even that is cheaper than machine replacement...
So I would say panel-accessible parts are common replacements. Generally, folks will suffer a hdd replacement rather than buy a new machine... Keyboard replacement is common and usually cheap. But if you've got to go scuba-diving in there, the price of disassembly/assembly along with the price of the part, is generally prohibitive.