I had one very similar, kitted out with a 111S Diffuser, Tigger Splitter, HID's, Hurricane induction, quick shift kit, remote stat, a Larini Clubsport box and a few other bits. I wish I had kept it. It was an early S2 and still lightweight (before AC and the comfort pack etc was fitted) and fun. It was also rapid! Also had a modified S1 I lost in a fire
Compared to the Z4.
Drive: It feels faster, having such low weight, it really shifts off the line, once you get to 80 odd though you can feel the engine running out a bit. 100+ and you notice it. But keep it where you want it to be and it punches well above it's weight (forgive the terrible pun) against cars with a lot more power. Over 80 and the Z4 is a better place to be all round, the extra power is just there, no down shifting etc.
Handling wise, stick some S1 geo on it and the handling will outclass the Z4 any day long. It will take a very, very good driver to keep with you in a Z4. I had Yoko's on my S1 and S2 and I never found the limit on the car, tyres got hot and sticky on SELOC days out, but never did the car not feel stuck to the road, and I mean STUCK. Unless you are in a Caterfield or above, the Elise is just pure mechanical grip personified. Overstep that though and they are prone to snap oversteer. The Z is much more progressive and the added weight helps with the predictability. I went from my Elise in to my Griffith and it was like going from a scalpel to a Bowie knife, this is what going from the Griffith to the Z is like. Everything the Elise does is instant, due to the light weight and stiffness.
Comfort is where my Elise was lacking. The S2 seats (I didn't have Probax) got very uncomfortable after a couple of hours at the most. The sound system was.. better than the S1 and both got very fatiguing due to the drone at motorway speeds.
Getting in and out of them, especially the S1, was a massive PITA. Though the roof got better, it was always a pain. But due to the driving position and cockpit, you always felt special in the Elise. In the Z, I sometimes get the feeling I am just in another BMW. But the Elise is very crashy, stiff suspension combined with, light weight and the ali tub, touring is great possible, but again can be fatiguing. Especially when you are wringing the engine. The Z you can just cruise.
My Z4 is actually the worst car I've had for reliability so I can't comment on it compared to the Elise. The Z4 lights are awful, the Elise was similar but still better. The Z4 wipers and heating are good, the heated seats great. The Elise was still very, very cold and I had a collection of cloths inside for demisting until the engine came up to temp and most of the moisture was gone. I'm sure the later ones are much better, but add in weight for AC etc.
The Elise being light was easy on consumables, but suspension was/is considered a consumable, coliovers lasted around 20-30k ish. Economy was actually worse than the Z on a run, maybe a bit better in town.
Living with the car day to day: (reliability aside). you can fit a fair amount in an Elise boot, small bags are the key, not big cases. I used it as a daily, instead of my TVR. It does come with the fear of GRP, someone hits it hard enough and the clamshell will be a write off, which is very expensive. I would say the Z4 is easier day to day.
Would I have one again? Yes definitely! Another S1 or S2, not the S3 which IMHO looks awful. Would I miss the Z, on the cold rainy days, definitely.
I have considered an Alfa 4C recently, but that is a pipe dream as a house is more important.