Whatever solution you pick, you should always have an offline backup. An online backup on the server it just too risky. If low cost is important, I would investigate scripted backups to one of your local machines, I think rsync only syncs changes, which should be cheap.
"Would increasing it to 2 or 4GBs really make that much difference to what are already fairly fast websites?"
Probably not if they are already fast. If you want to be sure though, I'd suggest monitoring the resource usage for a while. I believe there's a Linux command for it but I forgot, sorry.
Whatever solution you pick, you should always have an offline backup. An online backup on the server it just too risky. If low cost is important, I would investigate scripted backups to one of your local machines, I think rsync only syncs changes, which should be cheap.
"Would increasing it to 2 or 4GBs really make that much difference to what are already fairly fast websites?"
Probably not if they are already fast. If you want to be sure though, I'd suggest monitoring the resource usage for a while. I believe there's a Linux command for it but I forgot, sorry.