Re Seneca
When I said single engine was a non-issue in aztec compared to seneca, I didn't profess to be an expert - quite the opposite as the only time I flew a seneca was doing my ME rating and I suspect you are a much more proficient pilot than me. I just found that asymmetric you had to nail the blue line speed pretty accurately even lightly loaded (2 people plus the bag of ballast you have to carry for CofG) or the ground quickly got closer! I understood why low time private pilots sometimes get into trouble in twins - if an engine fails, it's likely to be an unexpected and somewhat disconcerting experience and I can see someone out of practice getting flustered and the old cliche of the second engine simply getting them to the scene of the crash faster, which was a good thing to appreciate.
In the aztec doing my IMC multi renewal, I can sloppily sort out controls while peering under goggles to see what I'm doing to the engines, work out approach etc and it keeps flying happily upward with only a casual glance to check that the ASI and blue line are still acquainted. I've had the benefit of a bit more time in the Aztec but it just feels to me as if it there's more time to take a deep breath and calmly enjoy a bit of unscheduled asymmetric practice and instructors have agreed it's much more forgiving.
The left is supposedly the critical engine and that's not really a problem for control but what is a problem is it also operates the hydraulic pump - I've practised manually pumping the gear down with it fully shut down but I don't fancy doing a late go-around on the right engine for real - I hope I'm not tempting fate by saying this!
On takeoff, it zips past red and shortly after blue lines so you'd have to time it really spot on to lose an engine between being too late to abort and blue line. I'm not sure how single engine altitudes compare but I take published figures for a 30 year old aircraft with some scepticism, the point is that if you need to maintain say 8000 feet to clear mountains, it's unlikely to be terrain full of friendly fields to glide a single into and anyway you can cover more ground looking for one with one engine than with none!
The seneca does win though on eurocontrol charges!
As for cost, I saw a pristine aztec F for double what I paid and I suspect your aircraft looks a lot prettier than mine, but the 70s charm - a friend described it as like an old Ford Cortina, and more importantly the fact that the elements attacking the paintwork aren't knocking thousands off the value, have grown on me.
I think we'd both agree though that the negative things people say about twins are generally somewhat misguided - at least in a twin you normally have to take a positive step to kill yourself by your own stupidity if you lose an engine whereas in a single there are circumstances in which no matter how good a pilot you are (unless you are cautious enough to avoid them all), it's going to be a very bad day.
Finally, the other benefit of flying a twin is that ATC assume you are a more proficient pilot and are more helpful to you and let you through when they might turn a single away!