Here is some good info about the Special Club from Brad Baker.
At one point in time the Special Club was really the 'who's who' of top grower Champagnes. At least that is what they were when they formed in 1971, but they started to lose their way in the mid-1980s when they insisted everyone make pure, precise, fairly stereotypical wine for the particular grape type(s) and village(s). The wines had to be good, but not too far off the normal path and they didn't want anyone to standout too much, be too different, or get too much attention. This led to a number of folks leaving like Selosse and then Peters. The club didn't want to change and soon membership became a rotating door. Standards dropped and outside of a few standbys, quality overall dropped to.
Recently they have become more open to new ideas and the Club's quality has increased. Some of the newer members are young, bright, rising stars like Mousse, Mouzon-Leroux, Goulard, and Remy Massin. The core are the long time, high quality members like Margaine, Gimonnet, Hebrart, Goutorbe, Bara, Chiquet, Lassalle, and Jose Michel.
Past members who are well known include Pierre Peters, Bonnaire, Jacques Selosse, Larmandier-Bernier, and Philippe Gonet.
For anyone who makes it over to Champagne, the Special Club (Club de Tresors) Shop is very well done and a great place to visit to purchase/taste. The Club also does a tasting during the 'Champagne Week' activities in April where all the producers pour their Club wine and a few other cuvees they make too.
In conclusion, the Club isn't what it once was, but is better now than it has been in at least a decade (probably more). Special Club does not denote that a bottle or producer is great, but a number of them are very good deals. Also, some of these sell for 30 Euros in France so they are fairly priced from that aspect. If the Club can gain some stability in membership and see some of the newer members continue to increase in quality then it could become something very special once again.
One other thing to add is that many of the Club producers now make a wine (or wines) that they consider above and beyond the Special Club bottling. At the start of the group, the Special Club bottling was always the prestige cuvee of the producer, but once producers wanted to produce a wine outside of the norm for the group and bottle it as a Special Club, things went sideways and many members left or grew uneasy. Members were forced to make sure Special Club was the top wine and that it met group standards for uniformity and expectations. This led even more to leave.
This stance was slowly relaxed a bit over time, but even up until just a few years ago, there were still a number of constraints on what you could and couldn't bottle as Special Club. Today, most of the Special Club bottlings are at or near the top of the producer's range and still tend to be an overall representation of what the producer can do without going too outside of the norm. Most of the more creative winemaking cuvees and wines focused on a particular expression (vineyard, village, grape, oak, etc...) are now released outside of the Special Club range. We will have to see how the younger generation of members responds to this.
I would love to tru the Selosse SC from years ago. In 2014 a 1979 Selosse SC sold for 740 Euros at auction.