As per the normal rules, one is suppsed to use base IQ. However, base IQ can
be raised, effectively giving a character better 'sense' rolls.  The thought
that immedately crossed my mind at that point (and the same thought that
occurred to you) is: How can one improve one's own senses? This is similar to
something that you have been fond of saying in the past: How does a person
will oneself to become taller?

But then it occurred to me: The IQ attribute is a composite of a great many
things: intuition, mental aptitude, problem-solving ability,
communication/social ability, experience, training, and senses. With that in
mind, I did a bit of a reality-check on my own senses and my own ability to
notice things.

When I first learned how to drive many years ago, I was pretty oblivious to
things going on around me on the road. I didn't pay attention to people
merging up ahead, cars moving up alongside me that I could see out of the
corner of my eye, and other subtlties of cars on the road. Nowadays, however,
I'm much more cognisciant of what's going on around me when I'm driving: I can
tell when there's a trouble spot up ahead and how to get away from it, and a
number of other nuances that I never used to pick up on. In a way, my
"senses"--in the "sense-roll" fashion--have improved even though my actual
physical senses--especially eyesight--may have actually diminished. 

It then occurred to me that I might simply have a higher "driving skill", so I
tried a few more reality checks. I reflected on how I'm much better at
determining if food or milk has gone bad when I taste it, and how I can pick
up on ambient noises (especially in machinery)           when I'm listening
for them, largely due to the reason that I know what to listen for (or what
_not_ to listen for).

I could probably go on trying to come up with obscure skills that might cover
all of these specific examples (Milk Appreciation?  Mechanical Diagnosis?),
but I think there's a deeper reason behind all of those specifics; call it
experience, aptitude, training or what              have you. The upshot is
that while my actual, physical senses may not have improved, many of the
auxilliary components of my mentality--the same components that are ancillary
to my senses and work in harmony with my senses--have indeed improved and the
the net effect is that I have more accute "sense"--once again, in the
"sense-roll" fashion.

So it makes sense to me (no pun intended) to use IQ as a basis for sense
rolls, regardless. Plus, it makes the game system a little simpler.