I've asked my father this who has been in insurance for 40 years.
Normally you can add bikes to your home contents. Most insurers wont want proof to their value. However, problems will occur in the event of a claim eg: then you need to prove their value eg: a receipt.
Firstly you need photos to back any claim, not forgetting frame numbers if still visable.
If you had a watch for example, normally as you say you would have a current valuation. There could also be clauses by the insurer that they must be kept indoors (not a garage) if you are insuring for a high value and they must be padlocked together.
My fathers advice was ring your insurer and hear their views as to having no proof to a valuation. One thing he did say is do printouts of what bikes have sold for on ebay. You could use these as a form of proof and current values, backed by your photos.
If your insurer is still not interested pop into your local high street broker and they should point you in the right direction.
Hope this helps a bit.
