At some point soon, most of you who have held back will be forced to make the change to New Blogger. When you get there (are Migrated), you may not have to change your template immediately or even for a long while.
Those of you with a heavily customized template can (sorta) keep it!
However, you can't quite keep your own--not if you upgrade! Sadly, if the time comes when you have to or want to change to a new template so that you can utilize the full range of new features in New Blogger, then you may as well realize going in that the template choices are few. You may find them all dull and boring.
Cheer up if you're dumping an attractive customized template! It will take work, but just choose one and let the system Upgrade your template. Later, as time goes by and you learn how things work in the new set-up, you can begin to make the changes in your new template so that it will resemble your old one.
Keep a copy of your old template for reference. You will be able to Copy and Paste portions of it into the new template, as well as restore the additions you made to your old css code that are not in your new template.