. I don't think I'll ever buy new again.
Agreed. Besides my 50mm 1.8, and a Sigma 28-90, everything I have added into the collection, has come only "new to me".
If you have the chance to rent a piece of glass that you want to own, then go for it. Nothing better than trying before buying, it's not like photography is the cheapest hobby out there. NEXT, after you have decided you want to add a piece of equipment to your bag, if you can get it used (and know that it is functioning as it should be), I see no reason why NOT to get used/refurbished.
The only BRAND NEW thing I have in my bag, is a Nikon D700 that was actually given to me as a gift (I'm still with her, and she is WAY amazing beyond her respect of my photography hobby), besides that, and my Nifty 50, everything I have ever bought, is used.
Until I can start bringing in money, based on photography, I will ALWAYS look for new/used first. Photography isn't paying my bills, it is just a hobby, so for that I am just a frugal kinda feller. I would LOVE to have a limitless bank account to apply to my "wants/needs:, but that is just unrealistic. There is NO SHAME in buying used, especially if it is a factory refurb.
Work SMARTER, not harder. Buying something that is factory refurb, at 1/3 the MSRP is a no brainer. Make the most of your self allocated budget: THAT MEANS DON'T BE AFRAID TO BUY USED.