Keep in mind that the arena maps will most likely be quite small. And I don't think the counter-strike comparison is in order. There's no 'gain' for a team winning a round. In counter-strike, if you've got one team which wins the first two rounds, they often end up having the powerful weaponry...
The cap point is probably to fix endless running in circles when it comes down to the last two guys.
I'm not overly impressed by this new game-mode, but I get the impression that it's not meant to be a 30-minute stretch on either of this maps.
Where exactly did you add the sprite code ?
(and can we see it ? :) )
I can also recommend the HLCoders mailing list for these sort of questions. If it's a known problem, you'll most likely get a good answer there.
Check this:
https://support.steampowered.com/kb_article.php?p_faqid=231
The recommended valve way to do it is:
1. Copy steamapps to somewhere safe (remove steam if necessary)
2. Install steam again (on a different location or a different harddisk)
3. Let it update - copy over steamapps
4...