Yes, that's right. The two mights are quite different.
The might in sentence 1 is a hypothetical one (I tend to call it 'unreal') whereas the might in sentence 3 is a 'real' one, since the utterance states a real future possibility.
Concerning the question in post #1, my advice to you is this: Use 1, not 2.
Since you use the word "hypothetical/unreal" here, I've got another question for you:
1) I
might say one of these sentences, depending on the context.
2) I
could say one of these sentences, depending on the context.
3) You
might try the gas station down the street.
4) You
could try the gas station down the street.
5) I
could be run over by a bus tomorrow.
6) I
might be run over by a bus tomorrow.
7) He was jailed five years ago and
could be released next year.
8) He was jailed five years ago and
might be released next year.
My comments:
a) Except 6,7 and 8, all other sentences use "hypothetical/unreal"
coulds and
mights.
b) "might" and "could" are
completely interchangeable in 3,4 (hypothetical) and 7,8 (real). They are
not completely interchangeable in 1,2 and 5,6.
c)
Although interchangeable in 3,4 and 7,8, "might" and "could"
do not sound the same in each of the two pairs of sentences. (3 vs 4 and 7 vs 8)
d) All the "might"s, whether "hypothetical" or "real", sound exactly the same. Likewise, all the "could"s, whether "hypothetical" or "real", sound exactly the same. (though I'm a little unsure about the "could" (real) in sentence 7)
Are my observations correct?