Darker is a relative term davidro.
If you've just been splashed with sound at a showroom, Spendors are going to sound kind of dark and classic Spendors are going to sound somewhat darker than tower Spendors.
Your ears adjust to sound similar to the way your eyes adjust to light.
One person's dark is another person's twilight, is another person's favorite type of light.
Subjectively, in terms of presentation, I'd say I found the towers a bit forward and they required an adjustment on my part to what they present compared to what my classic Spendor's have presented.
With all that said, I'll take the towers. They do everything the other speakers did well, including the BC1's quality midrange, and add to it without being overwhelming.
Compare those new-to-you Rogers to other speakers you've used and consider that the Spendors provide some of the same magic that Jim Rogers produced voicing those speakers.