About a year ago I upgraded RAM from 3GB to 6GB, which dealt with most of my multitasking and "large files in memory" issues.
About 2 months ago I bought a Samsung Evo 250GB SSD for under €90. This solved just about every other frustration I had with the machine - slow boot times, slow program load times etc.
The only issue I really have now is maxing out one core too easily and having the fan spin up loudly. Investigations reveal a CPU upgrade is possible.[0]
I have no intention of buying another laptop for a further 12-24 months, even if the plastic case of this one is held together with super glue and tape.
[0] https://community.spiceworks.com/topic/433227-asus-x54c-bbk9...
In any case, with an SSD, my boot times from cold start have been faster than coming back from hibernation were with rust disks. Plus, clean starts are less likely to leave things in a fubar state than the often-buggy hibernation
And if you're reinstalling the OS anyway, add an SSD (at least for the system files). This gives a substantial performance boost on most old PCs for under 100 $/€.