Merlin Passes - are they worth it?

Last year we forfeited a 'proper holiday' and bought Merlin Passes.  For 3 of us (Noah was only 2)  it cost us about £300.  So we made the most of them.

We went to:

Legoland Windsor (1 and a half days).  post 1  post 2
Alton Towers (2 and a half days)  post 1   post 2
Legoland Manchester (4 times - I think)   post
Sealife Manchester (2 times)




If you take these as face value costs (not including the half days) it would have cost:

Legoland Windsor (1 and a half days) - £139.80
Alton Towers (2 and a half days) - £95.85 x 2 = £191.70
Legoland Manchester (4 times - I think) = £44.85 x 4 = £179.40
Sealife Manchester (2 times) = £44.85 x 2 = £89.70

That's a grand total of:  £600.60

Had we not had the passes there is no way we would have paid this much money to go to the attractions, we probably won't have gone to Legoland Windsor and certainly wouldn't have gone to either of the Manchester attractions.

We would have gone to Alton Towers once as promised Noah he could go to Cbeebies Land.

We really wanted to do the London and Blackpool attractions but ran out of time.

So the question for this year is ........ do we renew?   It's going to increase to £400 as have to buy Noah a pass this year (even tho he will only need it for the LegoLand attractions) he's far too advanced for his age and I cannot get away with pretending he's younger then he is.
 
If we don't buy a pass we'd not do as much, I've given Ben the choice of Alton Towers or LegoLand and he'd rather go to Alton Towers (which also works well for camping in the Summer) so I think I may save the £400 and have a week away in the summer and maybe a holiday elsewhere in Feb half term if I can get cheap tickets for somewhere else.  I'd really like to book a Haven Holiday somewhere this year as I did miss it last year.

   Any suggestions for great places to take the kids that don't cost the earth?  Which holiday camps do you favour (preferably the north side of London).