The idea of so-called "investment dressing" has always struck me a marketing tool put out by the media to rationalize the cost of big ticket items. There is no doubt that almost any Hermes bag falls into this category.
This is not to say that I have not succumbed to the rationalization of "it is an investment in my future, I will wear it till I die" myself.
So is a Constance in this category? An investment piece? Well it is one of the most classic designs that Hermes makes, but it is a bag that has come in and out of fashion. If you love it, it will serve you well. I love mine and I will keep them always.
However if you are buying it to re-sell in a few years it will not be worth the same. The Birkin will hold value better in monetary terms.
It is a matter of the heart. Not a matter of the mind.