ML is a very good loudspeaker. To think that you should go looking for something better is childish if you enjoy what you're hearing now.
I first heard 'stats about 40 years ago. I ran a pair of X-Static EC-X loudspeakers (very similar to your ML 13a) for about 10 years. I loved the tonal balance but they just never imaged all that well for me. Like your ML, they were a curved diaphram electrostat. I paired them with some subs I designed.
In 2006 I moved on from them to some custom built Linkwitz Orions, which I still run to this day. The Orions have a very similar tonal balance to my old 'stats, but image extremely well. They are truly exceptional on voices and acoustic piano and they can deliver level and dynamics your ML 13a could only dream about. Level and dynamics are the one short coming of 'stats. You may think you have good dynamics, but you don't. Really.
The Linkwitz designs are mostly home-brew DIY systems, though there is a company in Europe that sells turnkey versions of the LX521 for about $20k. You can build the LX521 system, with amplification, for as little as $6k. It's an extraordinary loudspeaker system with even more dynamics than my Orions.
Don't look around to find someone who has them and go listen. It would break your heart.
Martin Logan vs. Everything
I have a pair of Martin Logan 13a. to me they sound incredible. The thing is I also like to spend time at hi-fi shops , whether they be brick and mortar or or online and it seems like those dealers think the Martin Logan are the weak Link in my system…
I’ve listened to Speakers twice and even three times the price and they don’t sound any better to me but I do have my room treated and everything is tuned just in my liking. my personal opinion is that Martin Logan has spent years perfecting what they do with the electrostatic speaker, and that it’s just not financially feasible for some of these smaller companies to try and do the same so they have traditional box speakers, which are great, but to me not as great as the Martin Logan .
so how wrong am I ? Fight me.