I've always wondered about older vehicles being allocated to less popular routes.
It's almost like operators are giving up on it and are going through the motions.

What if (and its a big what if)? An operator was able to justify a business case to grow a route and to do so by allocating new vehicles to it.
Almost like a pump prime of frequency and a new allocation of vehicles. 
I'm trying to think of an example of a route left to rot and maybe because its close to my heart - but the 71 is the one jumping out.
It went from an allocation of brand new 51 plate Presidents on the 21a to T reg acquired darts when the 71 was launched in 2006.
If that route was launched with a brand new 56 plate Scania or even a 55 plate Solar - would the 71 have been a success? Couple it with some marketing, advertising and something to soften the fact fares doubled overnight... 

We keep seeing that 'experimental' services aren't a success. Why? Is it pricing? Frequency? Timetables? Connections? Something else - such as the vehicle type? Or a combination?