As far as I know, loss of moisture is the only thing that would reduce the weight of wood. Bugs or fungus will eat the nutrients out of the wood and that will reduce its weight.

I've used hickory that's old to flavor and it seems OK to me. It's moistened anyway to make smoke.

Were going in two different directions.

Seasoning wood is to dry it and reduce moisture content so it burns with more heat and less creosote formation. Usually target is 15% or less moisture. Any additional moisture requires additional BTU's to evaporate the water. Dry wood is also much less susceptible to rot, mildew, and pests.

Smoking woods are species specific to get the distinct flavor of the wood. Wood is dried to drive off volatiles (which impart a "green" flavor) and to preserve the wood better. Chips or blocks are them rehydrated (soaked in water) to produce smoke (rather than burning hot and clean).

Yeah as GG has indicated you are not comparing apples to apples . Seasoning firewood to produce the most heat as possible from the density of choice is not the same as
that of producing the best flavour from the same product .

At first I thought along the lines of ewalk and ggoyeneche, but after looking closely at the question, he is asking about overly seasoned wood losing it flavor.

I had a pile of mixed hardwoods under a tarp and dry. It was alot of hickory and other woods. It sat there for about 6 years, always dry. Although the wood was completely dry, it was eaten by bugs and became light as a feather and worthless.

I see some of these indicators in his question.

Sassfras will keep flavor in wood mind get stronger over time makes good grill chicken.

Baymee: Good point Dude . Sorry Loger if I misinterpreted your question .If Bay is correct within his asumption then I would say that yes as the wood density lessons as it dries out it perhaps wood change the flavour it gives off when it is smoldered . I have to confess that I do not have a Commercial Style Smoker , but rather a Home made Smoker / Dehumidifier from a old fridge / freezer double door unit . Top is a Dehumidifier and larger compartment below is for smoking . I use Apple , Alder , Cherry and Mesquite along with Hickory as my flavours of choice. My Sons chipper is used to make the chips a fine as needed .
Let us know Loger if we have anwsered your question adequately Bro ? I would think that the drying process may in fact make the flavour more concentrated .

You did recognize my question and addressed my concern as to when does wood loose its value as firewood and BBQ/Smoking wood. I have tried to pay attention and rotate my wood and burn the oldest first. With a harvest of 3 of 4 cords green last winter, that put me in good shape. In the past at my grandparent's they had the choice to cut standing wood timing it to their need vs me finding wood that is cut or dead and need cutting as I am notified of I spot it.

Last, A Twist To BBQing! The best BBQ in town is flavored with green Hickory as soon as it hits the ground from Oklahoma. Gas is used for heating in large insulated custom built rotisserie oven/grills and a small amount of green hickory is used with rubs for flavoring. Also a friend was advised to burned seasoned oak for heat at his business vs expensive cords of seasoned hickory and add a small piece of green hickory the last 30-45 minutes of the cooking. I have tried their method using their personal small piece of hickory and rub with no luck compared to their quality. My best flavor and quality comes from mixing seasoned pecan (2 small sticks) and mesquite (1 small stick) on charcoals (6 lbs) to get even heat and their rub. loger

In PA, I would say that apple wood is the most highly prized smoking wood. But much less available than our abundant hickory and cherry.