Mostly I'm thinking here for DJ speakers at smaller
venues, such as wedding receptions. Sometimes
I plug into the DJ board direct, but sometimes
they just don't have a line out, or don't want
to be bothered.
Anyways, I'm looking to get a mic to face directly into
the cone (or maybe a bit off center) of the speaker
at close range (foot or less) and I'm thinking
maybe a condenser would give better sound
(frequency range, etc.) than a dynamic.
I've thought about dynamics such as AKG D440,
AKG D770, and Shure Beta 58.
But I've seen the Rode NT1A listed in advertising
materials and testimonials as being good
on guitar amps, and if I were to go this
direction I'd also be gettting a decent mic
for voice overs. The NT1A is listed as having
max SPL of 137dB, and I would guess this would
be okay for smaller locales such as receptions,
where they really don't blast it out.
Another option I've considered is the AT 3031
because of its high max SPL of 138/148, but
for the situation I've described, does anyone
really think I'd be dealing with that high of an
SPL?
Any thoughts would be appreciated.

What camera will you be using? A condenser mic for a speaker at close range will probably need to be attenuated before the camera's input, either with a MicATT switch or an inline attenuator.
Of course there's phantom power to think about but you had probably already considered that...
Last there's the risk of having a more expensive mic in that kind of environment (theft, damage, smoke, etc).
You might want to consider a dynamic mic that specifically has a wider, flatter frequency response. The D770 is listed as 60-20khz and is flatter than the Beta 58. It has a sensitive proximity range, which is a good thing in this case, but would require some experimentation in placement.
The Sennheiser e835 is listed as 40-16khz. The EV N/D 468 or the 367 would also be good choices in better sounding dynamic cardioid mics.

Given the SPL of the subject being mic'd, I'd also recommend a dynamic. Even an SM57 would be pretty good in this environ, IMO

For VO mics like that Rode, how far away should
the speaker normally be from the mic?

Don't you think the condensers would give a lot
better sound? Or not really?
I was a bit surprised to read that the
NT1a was good on guitar amps. Wonder
what a large diaphragm sounds like on
guitar amps?