The file format, from what I remember having looked at the content of Aerad floppy disks, is very compact. The B737-300/400/500 fleet we used to have had between 1991 and 1997 (I believe) a 96KB memory (that's Kilobytes, a total of less than 100,000 characters of memory). This was tight for our operation; we did kick out SIDs and STARs for secondary airfields. However, we got two database cycles in that, plus its 4k of workspace - thus, the data for a pretty usable operation around Europe.
Unlike bloatware inefficiently produced by companies such as M**r***f* and A***e (have you seen how much space a single Word page takes up?!), I'm pretty sure that the data standard has remained pretty compact.
It's true that you can't have too much memory. On the other hand, if you're filling it up with stuff that you won't ever use, then the extra memory is no more useful than the fuel in the tanks that you won't ever actually use - it just makes you feel a bit more comfortable, and makes somebody a bit of incremental money by virtue of you carrying it around.