Sol, Complinitor, and Jr's3800 were correct in their reasoning for changing out the T-stat to a 180...for all cars EXCEPT the SSEi (and other L67 powered Bonnies). The L27 and L36 Naturally Aspirated engines are prone to upper intake failure due to their plastic composition deteriorating.
HOWEVER, your car doesn't have the plastic upper intake manifold, so this is not an issue for you. The 180 T-stat is still very beneficial for our (L67 powered) cars because it helps keep the Supercharger cool, which increases longevity and power. The more the air is compressed through the Supercharger, the higher the operating temperature, and thus the less efficient the Supercharger. Heat robs power. This is why some turbo setups and Supercharger setups use intercoolers--to cool down the air charge of the turbo/supercharger, thus increasing air density--making it more efficient (more powerful). Any Supercharged vehicle owner can back this up. I will use my favorite example: between 1986 and 1987, Buick made the Grand National (turbo 3.
. The '86 GN didn't have an intercooler and was fast, but the '87 GN had an intercooler and was the FASTEST domestic production car in the U.*. (and Canada--they were made in Canada)--much faster than the '86. This is because they cooled the air down after it went through the turbo.
BADSSEi is running an intercooler and is running high 11'* in the quarter mile.
Since most of us don't have the $ to put an intercooler on our cars (not to mention they don't make them for Series I), the next best thing is to keep the supercharger cooler by any other means possible--180 T-stat, external cooling, etc.
I hope this helps you understand a bit of difference between the Supercharged vs Naturally Asperated reasons for choosing an 180 degree T-stat. It is recommended for all four engines (L27, L36, L67-SI, L67-SII) and is especially important for the L27 and L36 for reasons given by Sol, Complinitor, and jr's3800.
I think they just overlooked the fact that you are running an SSEi.