Some valuable covers with certain watermarking may actually need to be done so to ascertain the watermark and/or other pertinent identification factors.
That is a true statement and often overlooked as a necessary and fully accepted method of verifying what stamp is on cover. A dated cancel or other cover markings do not always allow for proper determination. When done, the cover is not devalued, rather it has the value verified since all now know what it is that is being valued.
Relative, isn't it? Drop in the bucket compared to the hobby in the US or as a worldwide whole. And since PSE charges a minimum of $10 per stamp and PF $27, I'm wary of your "all levels" claim
I just did an eBay
search and sort. There are 267 PSE graded stamps currently listing at or under $50.00 including shipping. The most recent one I saw (did not look for this, it just jumped out) was a self adhesive airmail from 2001. As some may know I collect C-46 and I have lost count of the number of graded copies I have seen offered, on eBay
or in person. At this moment you can buy on eBay
a MNH plate block of six for $7.96 including shipping or a MNH graded 100 margin single for $240.00 with free shipping. That PSE cert was obtained 12-15-2021.
...grading is just a crass attempt to commoditize...
Anything thing and everything can be subject to commoditization. The fact is that how the value of the commodity is perceived varies by ones financial situation. Some folks may be concerned over pennies while others can afford to lose a million plus on a stamp. A field of rice may have no value to you but a grain of rice has value to a starving individual. As to most anything, including the stamp hobby or profession, if not for commoditization a market would not exist.
Not that I wish to beat a dead horse over the fact many higher end classic collectors turn their nose up at low level (read little money invested) collectors nor seem to appreciate those whose very existence depends on planning well, counting pennies and a hint of good luck. Speaking of dead horses, even they have value as a commodity:
Lastly even plain old unaltered naturally and unnaturally polluted air has value, huge value at times. When the check cleared this household noticed a large five figure balance increase from selling just some "air space" above a New York building and that represented just a small fraction of the total sale amount in seven figures.
All that said, I must agree with wtcrow that if financial gain was the goal, the soaked stamp with a 98 or 100 grade would bring more return than the current entire cover.
FULL DISCLOSURE: I have not paid for a graded certificate nor have I specifically purchased a graded stamp because it was graded.