I think it's totally worth it, staying in zones 1-2 was never going to be an option for us as we're not millionaires!, obviously there are drawbacks, commuting is not normally too bad so long as you are on the tube or a good train line but you have less flexibility, when you are in zone1 you can always jump on a bus or taxi or in a last resort walk to where you need to get too where obviously if you are dependent on one line and there's problems on the line or you miss your last train home you can be looking at a slow or expensive journey, you tend to need to be a bit more organised particularly if you are in a '2 trains an hour' type of place.
Also suburban outer London, even the posh/'naice' bits does feel very different to central, different shops and choice of restaurants etc. Round our way (zone 4-5 North London) it's pretty average high street stuff most of the way, perfectly adequate but if you want upmarket bistros and designer clothes shops you'd have to pay megabucks to live in Hampstead or Muswell Hill or similar. Most parts even the lower end do have access to nice some parks, and the advantage of being slightly further out of London is if you have a car you can get onto a motorway and out to some 'proper' countryside very easily if that's your 'thing'....
As to where, depends on your definition of affordable (and 'good' for schools lol)? There are parts of zone 4-5 London that are cheaper than parts of Herts but for maximum value for money you are probably better off looking south east of the river, even so for a family house, garden and catchment area for popular school I would have guessed easily £500k + ....
Or alternatively maybe go even further out, places like Bedford or Milton Keynes are on on mainline rail to London so quick connection, close ish to your family, and you will be able to get a really nice family home for much less than anywhere in London? Not that they are particularly lovely towns but I guess it depends on your priorities...