Feedback score and price are usually the two things most buyers look for on ebay, as long as your listing isn't a wall of text and contains all relevant information then there will be very little difference in using a template.
A paid template will not hinder your sales and normally increase them(even templates can be bad which is why I meantioned paid.) It's up to you to decide if it's worth it.
I personally don't use a template, while it would be nice, I believe simply having all relevant information in a small bite-size form is best, or atleast I don't believe paying £50-100 for a good template justifys the almost marginal increase in sales.