(By the way I've upgraded the RAM size to 1024 MB of my VPS and now bitcoind is more responsive, but still far from the perfect!)
I guess my post was too long, sorry
disablewallet=1 disables the wallet cache, which is 1MiB. It won't save you much, but it doesn't hurt.
dbcache=4 decreases the other caches to 4 MiB, which by default total 100 MiB. Setting this too low might decrease performance, though... I don't know what a good number would be, but if DnT and shorena both say 4 is a good starting point, I'd trust them, and then maybe tweak it up a bit if you have any spare ram.
Its a bit unresponsive from time to time yes, but it holds 50 connections without any issues. Its just that the shells scripts I use to query data from bitcoind do not finish sometimes within 30 seconds. This will result in "unknown" values and as a consequence white lines in the pictures the node generates. E.g. last night at ~0050.