i went that route. from 185/65-14 OEM firestone FR680s to 195/60-14 BFG
tourings. big difference in handling and comfort. havent crunched the
MPG numbers, but i dont think they changed noticeably. definately worth it.

205/45-16 stock size of '01 SE.  I went for the same size Azeni's.
Well actually I think they are 10mm wider.  Don't recall the stock
Turanza model number but they are very expensive 3-season tires
that are about the only ones rated "grand touring".  They are
almost universally panned by the Miata community.

Both contribute.  And both to a pretty small extent.  My wheels
weigh about 20 lbs, my tires about 20 lbs.  So, why would the
wheels contribute but the tires not?  Frankly, there's a lot of
conventional wisdom, and not all of it is right.

There is no simple answer. Though all the above is at least
generally correct.

It is true that a shorter sidewall will generally be stiffer,
result in less squirm, and thus be more responsive.  And usually
harsher.

A wider tire allows for a greater contact patch which gives
greater ultimate grip.  And you may need a wider wheel for that
wider tire.  

Some talk about a greater wheel OD giving a greater contact patch
(picture an infinite sized tire and the contact patch becomes a
straight long line).  But I think (no prood) this effect is very
minor.  First of all, most of the time when you +1 or +2, you stay
with basically the same tire OD trading off short sidewall for the
increased wheel OD.

Many in the Miata community swear by small wheels which, all else
constant, are lighter.  And they attest to great gains in
performance.  I think a lot of it is power of suggestion (at
least for accel).  Though the reduction in moving mass will be
beneficial and I honestly do not know the magnitude of this
effect.  Plus, small wheels lead to much cheaper tires!

It all depends on what tradeoff you want, how much you want to
spend,  and the tires available play a major factor in that.  
There is no clear cut rule to go by.  Best to ask for experiences
as you did.  Go to miata.net and read through the "Tires & Wheels"
forum.  If you have steel wheels, I assume you have an older Miata
with 14"?  Then you are fortunate in that these tires are
super-cheap (though performance types are limited).  I'd consider
14" alloys for looks and a bit lighter weight.  And perhaps Azenis
for very high 3-season performance.  Another very popular tire is
the Toyo TS-1.  But again, check size availability.  I might
consider +1 to 15" for better looks and a shorter sidewall.  
Certainly no more than 16".  UHP tires are a lot more expensive,
though they vary.  But a UHP Azeni in 14" is dirt-cheap!

We have a general industry trend to bigger and bigger. It's 99.9%
driven by looks.

But check miata.net and you'll find more info, and opinion, than
you probably could want!

FWIW, I remember reading a Road & Track article ~10 yrs ago or so when
the big wheel thing was getting popular. They did a study IIRC with a
BMW M3 and compared handling, ride quality, noise, etc. with stock, +1,
+2, and +3 sizes wheels and tires. They pretty much confirmed your
theory of incremental tradeoffs with +2 being about the highest they'd
go in that little experiment.

Wish I could provide more info about that issue.

.

True, especially for those cars that only undergo short trips. In my case,
the car is constantly running/moving and I'll go through a tank of gas in
couple days, so the impact from cold startup isn't as drastic.

Pars
98 Civic Hatch

My 195/50/15 Toyo Proxes FZ4 seems to have very good rolling resistance for
performance oriented tires. They also last forever, but tend to get noisy
when hey get old (frequent rotation would be important on this tire). Also,
they have  very solid side wall (at least the 50 series does), which is
useful on a tight suspension. The solid sidewalls also help during a blow
out...it almost act like  run flat tires. One time, a nail blew-out one of
the rear tires while I was doing some radical driving at 150km/hr. I felt a
tugging on my steering wheel and thought something happened to the
suspension/alignment. So, I reduced my speed to 100km/hr and continued along
my merry way. After I exited the highway (5 km later), I decided to pull
over and inspect the car. I was shocked to find that I was driving on a
completely flat tire. When it comes to tires, I'd put rolling resistance way
down the list, especially when you consider steering feel, road noise and
safety.

Pars
98 Civic Hatch

CL.

Charles, of course you have to let us know what package you upgrade to.
I just bought OEM hubcaps for my "new" '92 Civic EX and will put the $
into parts. Sigh.