Are expensive nappies really worth it?

Yes, they are worth the money! I wouldnt get mine overnight in one nappy without the 'expensive' LLS superwetters and BB+ from HL...would be having to wake him to change, yuk!
On the other hand perhaps try a WNNN first? They are less expensive and do a lot of mid to heavy wetters perfectly well overnight.

You know what im gonna probably go against the grian but after months of soggy wet sheets the best thing that worked for us MORE than bedbugs,LLS,WNNN were huge pocket nappies with 6 boosters in them

Each baby is different so i would say try a preloved one before splashing out, izzy peed through bedbugs after a couple of hours