Of course without being able to examine your roof I can't address the specifics of your situation. But here's what I can tell you:

Pitched roofs usually sag due to issues with the underlying structure (rafters, trusses, joists) and not the sheathing. If you don't even notice any sagging, you should check the rafters to make sure they are structurally sound, but you probably don't need to worry about it. If the existing roof deck (the plywood) is in good shape, you should leave it in place. If you are having a new roof installed, you should only replace the pieces of sheathing that are actually deteriorated.

If you have a typical roof with asphalt shingles nailed into the deck with a layer of underlayment, a radiant barrier on the decking will have very little effect on heat transmission. It would absolutely be a waste of money to re-deck the house if you're doing it just for this. Please see this article: Radiant Barrier Under Shingles - Scams & Bad Information, and this one, too.

If you want to stop heat from getting down into your house, you should make sure that the attic is properly ventilated and use above-ceiling insulation to do it (increase what you have now, install another layer of insulation that has a radiant barrier on it, etc.). If you want to cool down the attic, you can install insulation with a radiant barrier under the rafters (and make sure the attic is well-ventilated).

As far as contacting someone for independent advice, a certified home inspector would probably be your best bet, if you want to pay for an independent inspection. 

Basically, to answer your question, I would not recommend fully re-decking the house with Radiant OSB.

Hope this helps.