The problem I have with fire in a unit of templeguard is that you can't use burning head legally. It's a direct damage spell and has to hit one of your own guys. While fire does make up for the lack of skinks. Picking another lore and bringing skinks would be even better. I'm not saying that to be flippent, but more because we are talking about things being effective, not purely fluffy or fun or another similar reason.
Edit: You mentioned burning head before, the refresh button seems to have taken it away. I'm guessing you realised it's not legal to be used in a TG unit, which is why I asked about the unit you run in. I've seen a few people running slaans in saurus units. It opens up one of the better spells in fire to be used, and you can get out of dodge if you there is a dwellers or purple sun coming up. Fire just isn't for me I'm afraid. I'm using 40 skinks skirmishers currently, which I might up a bit after seeing how effective the skink skirmish army of doom was at the warington warlord GT.