Not sure if this is what you meant. I'm no template buff either but here's what I came up with. Seeing as the colon was the problem I took it out of there and made it a separate test. But for the life of me I can't get the space to stick other than putting it in front of the title field. It still seems to get swallowed when no series is present.
It just puts the title if there's no series,
if there's a series and series index>0 it formats it with the leadzero and decimal in brackets,
but if the index is zero it puts out nothing.
And last if there's a series to begin with, regardless of index being zero or not, plant the colon.
Code:
{series}{series_index:0>6.1f:'cmp($,0,'','',$)'|[|]}{series_index:test(:,)} {title}
I'm sure the real template wizards can come up with a solution that doesn't need the double inclusion