I strongly disagree with the criticism of the Gan Eden name. I believe that negative associations with kosher wine among the cognoscenti are a thing of the past (and you're not aiming for the mass non-kosher market). The Gan Eden name carries a great deal of good-will among kosher consumers. Don't forget that Gan Eden wines were still around until around 5 years ago, so even with the recent explosion in the premium kosher wine market, there is a significant percentage of consumers who know and love the Gan Eden brand. And those who don't will hear about it from their friends, who will be hyped up about Gan Eden's return.
As for price, it's hard to say as generally, the QPR of kosher California wines has fallen WAY behind Israel, Spain, and South America/Australia (on the low-end side of the market). In fact, with the introduction of Vignobles David, even France--which has always offered the worst QPR with really crappy inexpensive wines and stratospheric prices for better quality--has a far better QPR offering than anything on the market from California.
I don't think it would be smart to copy Covenant, as Covenant came to market at a time when big Nappa cabs were all the rage and he was basically the only game in town. Now that he's established a loyal customer base, he's able to sell those bottles despite the high prices.
Four Gates doesn't offer much assistance either as he only makes ~400 cases a year, doesn't want to expand, only sells directly, and has a loyal following that buys up everything he produces faster than hot cakes.
Hagafen has been around forever and has a loyal following, but I don't think it sells that well at the retail level. I wonder what percentage of his wines are sold direct or through restaurants (where they're a staple due to their mevu status). In any event, his prices cover the full range, so I don't think you can learn much as to where your sweet spot is in reentering the market.
Herzog is of course the 800lb gorilla, with decent but uninspired low-priced table wine, a lineup of reserve wines that are usually good, but rarely great at mid to high prices, and some really great wines at insane prices. Herzog is able to get away with it because their muscle assures them prime placing on store shelves and restaurant wine lists. Also, their name recognition makes them a go-to wine for the masses when looking for a "nice bottle" to bring over to a shabos host.
That leaves Shirah, with which you are of course intimately familiar. I think Shira has done a good job pricing their wines as exclusive but not insanely overpriced. They've added lower-priced offerings as they've ramped up production and begun retail distribution. Assuming your wine is as good as theirs (which I have every reason to believe given your track record), I think your best bet is to follow their pricing model and come in at the $30-60 bracket. It helps that you're focusing on different varietals/styles, so you're not competing with Shirah head on.
Once you expand, I really hope you can make some very good Cali wine for the $15-30 bracket, as it's a gaping hole in the world of Kosher wine. Although you mentioned the LR Cab, which you sold for $40, I seem to remember some amazing Gan Eden wines at around $20 or so.
As for devaluing the Gan Eden name, anyone who tells you that a great $50 Cab would devalue the brand is simply an idiot.