Upload & Sell: Off
I didn't have the opportunity to rent or inspect the lenses or support gear I bought in person prior to purchase. My suggestion is that you simply do a lot of online research, talk to people on forums and then bite the bullet and invest in the gear you can afford to achieve what you want to photograph.
Lenses can be rented but carrying gear isn't available for rent as far as I know.
A lens is a big investment, but you don't lose too much if you sell it second-hand in good condition. Camera bodies on the other hand - my 5D3 is probably worth $1k less than what I bought it for earlier this year... on the other hand I've taken over 10k photos with it, so 10 cents per photo is pretty good value for money.
Photography is an expensive hobby.... first world problems are such a drag ;-)
Thanks for the updates penpro and anakha.
I wish I lived in a larger city where I would actually be able to check out the more 'exotic' gear in the store. I hate making key decision somewhat blind. As I am considering a substantial change to my kit, it isn't economical for me to consider renting everything to try it.