Average attendances per match are way down. Don't know about overall.
The ECB should be spending money on subsidising tickets and paying to get the sport on FTA instead of a vanity project which is already doomed.
http://birminghambears.com/news/bears-continue-growth-natwest-t20-blast-attendances/
Same story ever since they they re-branded judging from my Google search. I think that's probably as much due to the ECB getting away from the daft 'fixture block' thing as anything though.
I agree with you that mothballing grounds like Essex and Somerset for T20 is short sighted, two divisions with coverage and talent massively skewed to Div 1 (i.e. the Premier League) would be best for me. Still think that this new 2020 revolution is better than the current fornat if the new broadcasting deal is what we hope for though.