Some observations going different ways on your question:
In favor of the Sound Odyssey mods
1. I have dealt with Brice Donnelly and, in addition to being courteous and helpful, he is a stand-up guy. He encouraged me to buy a Music Hall CD-25 for sale here on the ‘gon that he had previously modified, knowing it would cost him a sale to me of a substantially similar unit (I bought the used unit).
2. The MSRP of the stock Jolida 100A is $900. The Odyssey Stage 1 upgrade is $1095. For slightly less than $200, you get a lot, particularly the clock and power supply. True, you may find the stock unit for less than $900 from discount sellers, but the upgrade still represents a bargain in terms of the labor and parts cost. Sound Odyssey also includes shipping in its price. I don't have the technical knowledge or listening experience to comment on Steven's opinion that the clock is not that significant.
3. I bought my CD-25 modified, so I never heard the stock unit. Therefore, I can’t comment on the improvement made by the mods. The modified CD-25 is clearly better than the mid-fi, 5 year-old DVD player I had been using as a player, but the units are too different to draw any conclusions about the benefits of the modifications. (I would like to compare my CD-25 to a stock unit and to other CD players in its price range to get a better idea of its absolute quality and its relative value.)
4. As Readster suggests, the improvements aren’t likely to be as dramatic as the Sound Odyssey ad suggests. Like a lot of modifiers’ ads, the copy has a breathless quality and slightly over-the-top claims.
Against mods (in general)
5. A number of posters here on AudiogoN have suggested that modifying the Jolida changes, rather than enhances, the qualities that make it an attractive unit to begin with. I suggest you track down these comments and e-mail the posters for more information.
6. The people who argue against the mods say that simple tube-rolling is less expensive and doesn’t permanently change the unit. Don’t like the new tubes? Try different tubes or go back to the stock tubes.