re. the popularity of singles vs. the popularity of doubles:
How many people in the UK would be able to tell you that Andy Murray won wimbledon this year?
How many people this time last year would have been able to tell you that Jonathan Marray won wimbledon last year?
So in my opinion you have to look at what the reason for the LTA bonus scheme is... If it is for helping players to gain a higher ranking and become household names within the UK, then no it probably shouldn't be extended to doubles (and certainly not futures doubles), if it is to help players make a career out of playing tennis then yes it probably should be extended to doubles.