We also train at a school and so have a similar problem re: bounce. If anything it's poor practice for the bowlers, who are going to be bowling all the wrong lengths come the first game of the season, when a decent ball from winter nets is a long hop and gets spanked.
Like has been said, it mostly depends on who turns up. This year we've had a surprisingly good turnout and so I haven't needed to bowl much (a blessing for all involved), but also the school we train at has quite a few lanes - too many for us. So, we get chance to use one for just throw downs, actually having good practice with a partner. We then bat in pairs when in the bowlers nets for 20 minutes a pair, so probably get about 10 minutes each. It's quite convenient for me, I open the batting and am second choice keeper so need to keep my eye in for the couple of times a year I need to keep. I open the batting with the first choice keeper, so mostly I partner up with him and we can get a decent batting and keeping session in.
This is all very dependent on who turns up though, and I check we have enough bowlers in the nets first. I don't just wander off and do my own thing. And I openly admit I am biased, I'm not a fan of nets indoor or out and would rather have throw downs or targeted practice.
The social side is just as important though, and we always end up in the pub after for a few. This year we have tried a Sunday lunchtime session, and it really helps with the social side of things, people are more likely to stay afterwards compared with training at 8PM on a Thursday for two hours or something.