Right let's get this unreliable thing out of the way. Older cars had K series powerplants, these do suffer from HGF due to a poor design and poor levelling on cylinder liners. Most of these problems can be fixed by running a PRRT. Keep and eye on them and love them and it should be ok.
Later Toyota engines did away with HGF, and 99% of problems are gone. There was an oil starvation issue, prompting failures on cam lobes, this only seems to happen on tracked cars running sticky tyres, not a problem on the road I ever heard of. Can also be solved with a baffled sump or extra remote oil pressuriser.
I had a series 1 sport 160 (K series) as a daily driver, s2 with a supercharged Honda lump and a s2 exige S - both as weekend and track cars. Total breakdowns = 0.
The handling on an Exige/Elise is in another world to the z4, partly due to layout, unequal length double wishbones on each corner, but mainly because Lotus know how to setup a chassis.
You would miss the everyday usability of the BMW engines though, most of the Elise engines need their necks ringing to get the most out of them, but that's kind of the point. The Elise works in spite of it's engine and the z4 works because of it I would say.
They are noisy, but again that adds the the experience. Roofs are obviously all manual in the Elise, but you can remove an s2 roof in seconds from the inside so not an issue.
If you have a commute of less than say 40 miles each way it's no issue, I drove my series 1 all seasons (snow and all) on a 70 mile round trip each day. Without doubt z4 is more comfortable, but don't believe an Elise can't do it, its just whether you want to do it.
Boots practical too, you just need to be a creative packer!
The Elise is an awesome car, so is the z4. They can both do the same things as each other, just in different ways.
Love my zed, but still miss my Exige every day
