A question on this matter: is there any rule about reduced ECL mixing 2 template/species both with ECL 1+?
In some cases, it's fine to sum up correctives granted the power gained to not overwrite each other.
On other adding a template is may be reasonable from a Story POW but unfeasible without a reduced ECL modifier.
A simple example: Unholy Scion is a powerful template, finely fitting a lot of races and RP situations... but with some it's not sinergic... a unholy scion drow will be at ECL +7 (!) while the drow side will be giving really nothing aside a couple more SLA (weak too).
So: any regulation on this matter?
Unfortunately, to my knowledge the answer is no. The only option you have is to make a combined template and run it through Savage species's acid test, but that is totally DM dependent. Also everyone is going to have a different opinion on what the proper LA should be depending on your optimization skills and book sources.
I know in my current group the DM has determined the werewolf template one player has and the Gloura race for my character was too powerful . The werewolf template is pretty weak and I would never take it unless there was a RP reason. On the other hand the Gloura is good, but when I was forced to convert to human the power of my sublime chord build greatly increased and everything lost was easily restored with additional spell progression.
In the end you basically end up with a handful of templates and races that are worth playing despite the LA, and even less for spell casters. Level buy-off expands this list, but in games I have only ever seen it applied to the already short list of worthy templates to make them even more powerful.