You can separate blockquotes without html elements by using comment markup <!-- --> with an extra whiteline between the blocks:
> Imagination is more important than knowledge.
<!-- -->
> Never think of the future. It comes soon enough.
<!-- -->
> Anyone who has never made a mistake has never tried anything new.
Of course you can use any HTML elements you like as well (as noted by @pepoloan):
> Imagination is more important than knowledge.
<div></div>
> Never think of the future. It comes soon enough.
<div></div>
> Anyone who has never made a mistake has never tried anything new.