It is indeed a bad idea to buy a expensive tool like a scope for only 1 specific need in a project.
When you go buy something like a scope, try to think into the future a bit. Look at your existing scope and think about what it is missing. Then find a scope that is really good at those things.
The perfect scope for all uses does not exist unfortunately. So i find it is a good idea to have multiple scopes to cover all those cases. So for me personally i slowly accumulated a few scopes:
- Agilent MSO6000: 4ch 300MHz, pretty average capability scope, nothing special, but it boots fast and is fast to set up for mesurements, gets most jobs done quickly and efficiently.
- Agilent MSO9000: 4ch 4GHz behemoth running Win7. It is more cumbersome to use, but covers things my main scope can't do. It has 1GPts of memory, it has tons of bandwith, it supports active probes, can serial decode anything under the sun, can do fancy math..etc
- Some old HP Sampling scope boat anchor: 2ch 20GHz, old, huge, loud, power hungry, clunky. Only reason to use it is when you need the bandwidth, horrible scope otherwise.
- Owon HDS200: 2ch 200MHz nice little portable scope that is barely larger than a handheld DMM. A bit annoying to use due to lack of knobs, but allows me to take it anywhere while still being capable enough for most tasks.
So in your case you likely want to buy a high bandwidth scope and go for the fastest thing you can get. Make sure to keep active probes in mind. Anythyng >100MHz is tricky without them.