"or you're stuck in a CRJ, there's no way of upgrading. Then I have to ask - why would you pay extra for Latitude"

That's why I buy T+ for my western commuter routes (regular fare or pass) because of too many DASH-8s! and just short-haul so bearable even if a front cabin is available.

But I buy Latitude (pass product only) for:

complimentary or any certificate upgrades (100% success)--sitting in a comfortable seat for transcons is appreciated
last minute T+ fares can be almost same or more as Latitude fare (and I often fly last minute--this is a marginal benefit as I am sure I could plan better with just a bit of time and thought--but hey sometimes I don't want to have to think)
free meal (marginal benefit)

I think it is reasonable value as it comes (ultimately) out of my pocket. I think there is better value on F and C class travel on domestic Air China flights mind you!