OT: looking for advise on laptop upgrade

[Juan R. de Silva]

I have Dell Latitude D820 laptop with Dual Core 1.8GHz CPU and 1GB of 
RAM. The laptop is slightly over 6 years old.

Until recent I was satisfied with it. However with advent of new 
technologies it started performing poorly with DEs like KDE4 or Unity. 
Since I do not consider switching to neither Xfce nor LXDE, the only 
choice I have is either to upgrade RAM up to 4GB, which would cost me 
with taxes around $80-90, or to buy a new laptop. 

However I'm not sure on 2 things: 

1. Would such RAM upgrade actually give me real significant burst in 
performance? 

2. This one is a tough one :-). 6 years old laptop could actually die at 
any time leaving me with 2 not need memory sticks and lost $90.

So, I'm trying to make up my mind, whether to upgrade RAM or to forget 
about it and to save $80-90 rather adding them to buying a new laptop.

Would somebody give me an advise on the subject and/or share his/her 
related experience, please? At least on the first item:-).