I changed my mind. Subtypes are a very important aspect to socionics.
For example as an IEI-Ni, I'm definitely most attracted to SLE-Se rather than SLE-Ti.
Also, there is just too many differences between the subtypes to ignore them. I thought this difference was subtle and in a way, it is. But it's kinda like having 3 different major buffs in world of warcraft - which can be a huge deal you know. It makes quite a big difference between identical types, I'd say between 15-20% (rough estimate).
I'm the more withdrawn 'lost' type of IEI, the type that's more stoic and less of a people person, Fe subtypes are just different. They're more cheery, bubbly and enthused. Also IEI-Fes can be extroverts in the MBTI sense. I don't think IEI-Nis can be extroverts.