Basic rule of thumb is avoid the valley bottoms. I lived in Waterfoot for 6 years below the grammar school and it was OK. Been in Weir for 10 years now and live living up there.
Rossendale is generally not a bad place to live, great for mountain biking, good access to the motorway network and close to places like Manchester.
there's a lot of snobbery about Rossendale, which is one reason why house prices are cheap, especially as you get further from Rawtenstall and the motorway (which is a good thing in my opinion as there are some good deals to be had).
Most of the bottom feeder do reside on the bottom. there's also a good mix of housing across the valley with big mill owner style houses mixed with terraces and new build, something I quite like although for those who aspire to living in a gated community it's not so great.
have a look on Google maps, you'd be surprised how much of Rossendale is open countryside, you just don't see it driving through the valley bottoms.
For me I'd give Stacksteads and the centres of Bacup and Waterfoot a wide birth, not sure about the villa you mentioned, I know where you mean but wouldn't necessarily be my first choice. If it were me I'd look along Burnley Road East from Waterfoot towards Burnley and Burnley road heading north out of Bacup to Burnley.
The underlying issue with the valley is it used to be very industrial with hard people doing nasty jobs but working hard. The industries gone and you've now got the descendants of those tough people but without the work ethic stuck where there descendants lived with few prospects. It's happened in lots of post industrial areas, the upside for Rossendale is that there are also a lot of new people moving into the area bringing money to an extent and diluting the less reputable people.
Probably going to get flamed for putting it in those terms but that's the reality. Still a great place to live and it is slowly getting better (apart from the roads which are not good).