Complex sentence: As a general rule, Graftons are now regarded purely as collectors' items (i.e. for display purposes only) because they are so easily damaged, which detracts from their monetary value.
Split into simpler sentences: As a general rule, Graftons are now regarded purely as collectors' items i.e. for display purposes only. This is because they are fragile and very easy to damage, which detracts from their monetary value.