"Smokeable" and "worth smoking" are two entirely different concepts...
To me, an aromatic that has sat around for a decade may still be smokeable, but it may not be worth smoking.
In a best case scenario, all of the humectants and a lot of the added flavours have evaporated, leaving you with neutral tasting tobacco with a hint of aroma and a normal moisture level.
Worst case scenario, the humectants/flavours have destabilized and negatively affected the flavour. The tobacco has dried over time and it tastes like shredded newspaper or worse again!
It is certainly a philosophical thing. Do you subscribe to "waste not, want not" or do you believe that you should seek for the best flavour possible with every single pipeful?
If you subscribe to the former, then smoke away. If you subscribe to the latter, then you will probably be better served with another supply of tobacco...
Some of us are really sensitive tasters and others have leather tongues. Some of us live for OTCs and others are highly discriminating. Only you can tell what will suit your tastes.
In my own personal experience, I have never ever been satisfied with an aged aromatic. (Or an aged light English for that matter!) The flavour becomes far too subdued and you miss out on the intended aromas - therefore there is no point of smoking the blend except for pastime and nicotine consumption...