This is not a difficult question, most will say the more the merrier. YES! In theory, more RAM helped to “speed” things up. The questions are what kind of applications? And by how much?
On a VPS or dedicated server, you can buy more RAM or some called it ‘memory’ somehow to improve performance but you are buying, they aren’t free. When you add RAM, do you know the limitation of the OS? The applications? Adding more RAM to a 32bit OS, might not improve the situation. Because there is a limitation on the OS.
However, if you have a database has a lot of transaction, more RAM will help. But if the database is simply serving web content and does not have much transactions or updates. Anything at 4Gb is probably enough.
Here is my point, understand the server’s performance is relatively important. Paying more to buy more RAM every month might not solve your problem. On the other hand, should you pay more to buy more RAM to get rid of the bottleneck?
Actually, it is a debatable question, on many occasions, it is the ‘feel’ that counts. Metrix on performance are usually in very detailed value like millisecond (ms). Unless the gap is big, otherwise it is difficult to tell with a pair of naked eyes. So, understand your applications. Not forgetting RAM too has different speed, a larger RAM in capacity but slower speed or a faster RAM with lesser RAM is a debatable question too. Maybe in my next discussion.