Edit Quote added: "And I assume you're coating your profiling targets the same way as your final prints, prior to measurement?"
I had a discussion with Paul Morales (Breathing Color's profiling expert) on this subject a few months ago and, perhaps counter-intuitively, he advocated the opposite approach:
"To answer your question about varnishing: Do not coat the targets. When the targets are scanned with the spectrophotometer, the values registered are compared to a data file of the correct values (in referring to each individual swatch and their correct color value). If the targets are coated, these values will have significant differences when registered and the profile may over-compensate the value shifts. This could result in overblown colors, or washed out colors. While I have heard of a few cases where targets were coated and the profile created was acceptable, I personal prefer the consistent results uncoated targets provide. Remember, the coating brings out the color even more (higher density and saturation), so starting with strong accurate color is the best way to achieve the optimal end results."
I've just run a couple of profiles on Lyve canvas on my iPF8300 with the new i1 Profiler, one as initially printed and the second on the same targets coated with Glamour II. Predictably, the gamut volume and extension of the coated profile are significantly larger throughout, and very substantially so below about L:50.
I haven't yet had time to run any comparative tests between the two other than a very quick test strip with the latter on a difficult and thoroughly unrepresentative image but, with both prints varnished, the shadows and midtones do seem to be more open and detailed than with the 'uncoated' profile, though there may be some reduction in saturation. Unfortunately, until I get chance to run a controlled comparison with a more useful test image, I can't say which is the more accurate.
I'd be very interested if anyone has run a full comparison between the two alternatives, or has any further comments on Paul's recommendations.