I've been buying MAC for 20 years, but until I went on my binge last year I mainly just bought a few lippies and an occasional quad and used them up. My oldest items are a couple of years old, so I don't feel like anything is ancient. The official shelf life on lippies is 2 years but I've never had one go bad, even when I've used it for 3 or 4 years.
I'm quite proud of myself for scaling back my buying so much in 2013: Shell Pearl, Once Upon a Time and Aztec Brick from YOTS, Flatter Me and Oh, Oh, Oh from AG's, Definitely Defined, Fiery Impact and Opalesse from ED2, Heroine and Ablaze from Fashion Sets, Eclair from BB, Bare My Soul Quad, Caliente and Feel My Pulse from TR, Adored, Fever Isle and Narcissus and two HG items from Erine - Marine Life and My Paradise. Twentiesh items - lots to those who don't love makeup but very sane compared to last year's damage.
I don't count items like foundation/tinted moisturizer, primers, mascara or powder since they're staples and get replaced regularly. I just got back from the US and stocked up on all of these while there.
As for falling in love again, I'll always love Viva Glam 1. I can understand why they're relaunching it for a whole new generation. I remember the launch - it was my first ever MAC purchase. I also wore all my EDES again in a single week - still love those. I've been working on rotating my makeup all year since I'd only tried some items a handful of times. Apart from some bright e/s and lip pies that I don't wear often but am happy to have for when I want them (they get called into service for performance makeup for my daughter and her friends), I try to make sure most items get regular love. I do have some blush that I almost never reach for and could probably let go of:
Early Morning
Plum Foolery
Fleet Fast
NARS Joie de Vivre Palette
I'll make an effort to pull these out more this fall. If they don't get more use, I'm purging them. I'll give my youngest the NARS palette and hand over the other items for my 18 year-old's friends. Every time I do a trimming of my collection my daughter puts a pic on one of her Facebook groups and it's like feeding time at the shark tank. LOL
I love my collection but like it even better when I keep things to what I really enjoy.