Surfing around different blog sites, I've noticed that many bloggers are moving to Wordpress. I wasn't aware of WP when I started my blog; if I had known about it, I may have gone that way from the beginning.
Having forked out A$90 to MT for the privilege of getting support, I won't be moving anytime soon. The new version, 3.14, combined with MT Blacklist, has (for me) fixed the problem of comment spam.
I note that some WP users are having spam problems.
Also, I've invested too much effort in the templates to change now.
MT will force the change when it brings out a new version and wants more money for it, and / or if the new version requires extensive modification of the templates. I predict that will happen within 12 months.
Keep up the great work on your blog. Best wishes WaltDe