For the most part, these items will be worthless as far as investments go because of the vast quantites on sale. Only rare, limited edition items are likely to have any real value in the future. A lot also depends on the make as Thisismoney explains:-
Companies granted a Royal Warrant, meaning they are used by the Royal Family – such as Royal Doulton and Royal Worcester – can use the Royal Coat of Arms. But they cannot lay claim to the ‘Royal Cypher’, the EIIR signature.
Other collectable firms include Wedgwood, Royal Delft, Coalport, Spode, Moorcroft and the now-defunct Shelley.
When it comes to Diamond Jubilee coins and postage stamps, the only ‘official’ commemoratives are offered through Royal Mint and Royal Mail.
Other Royal valuables occur when an error has been made, for example some 52p stamps printed for the wedding of Edward and Sophie in 1999 are not perforated correctly and these are now worth around £1500.
Having said all that, beauty is in the eye of the beholder, and there are plenty of commemorative items for sale, from teddy bears to tea towels – and if you are visiting Aberdeen, you might be lucky enough to spot the “Old Aberdeen Diamond Jubilee” tartan, created in honour of the Queen’s visit to Aberdeen this year.
So to sum up, mass produced items are basically a waste of time as far as investments go. Rare or limited edition items are the things to go for, made by a recognised name, or a product with some sort of error. Items also need to be kept in pristine condition, even a small crack can render it virtually worthless.