I've been looking for a single rope to use on scrambles and ridges. Is it worth getting a lightweight rope that can be used for climbing? (30m mammut serenity or similar for example) - or is it not worth the money.
I'm not 100% sure what you mean - do you mean I want a rope for scrambling and should I go for a 50m rope so I can use it for more general purpose climbing?
A lit wt dry treated single would do everything - scrambling, alps, rock climbing - I agree there not cheap but they are multi-purpose and let you do many things with one rope.
The 1st rope I bought was a 50m x 9.2mm mammut revelation and used it for rock climbing and alps.
If you think your not going to use it for rock climbing then a 30m skinny single may be more your game. You could also use a 30m half rope for scrambling and alps etc if you wanted to cut the cost and weight but you need to be mindful that it is a half rope.