Product Upgrades. Worth the Money?

Many companies now offer upgrades. Monarchy,Rogue,and Odyssey offer such packages on their amps, as does Madisound on crossover parts.
What sonic improvements do these upgrades provide? Could we tell the differences blindfolded? Have you purchased these upgrades? Would you do so again? Have you recovered the additional costs on items sold used?
Pragmatist- I have upgraded my DNA 0.5 to Rev A+ thru SMc Audio. No question that it is worth the cost and I would consider going the full Rev A gold route when resources allow. Better definition, soundstaging, imaging, deeper, tighter bass. Better in every way. Not selling the pair that I am using for bi-amping, unless I upgrade my speakers or add a powere sub, when I may no longer need the extra oomph. With respect to $, I know that I sold a DNA Rev B for more than what I paid for it (bought it already upgraded). However, I would hardly expect to recover the full cost of an upgrade/mod, just as I wouldn't expect to recover the full cost of a new or used purchase, unless I got very lucky.
Are upgrades worth the money--yes...and no. I applaud manufacturers that offer upgrades--even expensive ones. My reasoning is simple. They continue to develop the product, and allow those developments available to their customers--without them having to buy new. Are the upgrades worth dollars per sound benefit? Is a Totem Arro worth $1000, is the Wilson Grand Slam worth $75k? Only the buyer can answer these question. However, buying from companies that have a history of offering upgrade paths to the newest technology tells me two things about that company. First, they are continuing to develope the technology and second, they are not abandoning their customers with total redesigns that then obsolete the equipment they recently bought. Whether you buy the upgrade or not is one thing--but at least having the option is important to me. There are a few companies out there that have told us repeatedly "this is it--the ultimate and built on a platform to be upgraded to all eternity". The next year is a new model--the old model is abandoned--never to be upgraded. In a more direct answer to your question--yes I've upgraded. Yes it was very clear as to the difference, and yes it was worth the price (at least to me). I would do it again (at least with the same company).
What Swampwalker said! I had a McCormack DNA-0.5 upgraded to Rev A Gold by Steve M. at SMc, and it's as good as what Swampwalker says. Was it worth it? Definitely-- this is a reference quality amp. I'd have no trouble at all identifying the differences between the stock and upgraded amps in a DBT. Cheers. Craig
Yes, it depends. The two relatively expensive upgrades to my Electrocompaniet EMC-1 MkII are definitely real sonically.
Whether they're of good value depends upon the resolution of a system AND one's preferences. Sometimes you can perform these upgrades yourself, and save considerably. Not always.