The local meaning here is perhaps more natural, but I don’t think it’s necessary (I’m just giving the general sense): “Hear me Apollo, you who are perhaps in Lykia, or [then again] I in Troy – but wherever you are, you can hear a man who is in need, just as I am in need now.”
“you who might be in Lykia, or then again in Troy”.
I don’t see that the local interpretation is absolutely necessary.
But here we are, defending the other’s position against ourselves…
An addition to my post above on what Denniston says about ἀλλὰ γάρ/ἀλλά…γάρ: From what Denniston says, if I understand correctly, what follows is that in this combination (ἀλλὰ γάρ/ἀλλά…γάρ), γάρ never expands something that precedes, but it always accompanies something either in the same main clause (in which case it just emphasizes ἀλλά) or in a following dependant clause (anticipatory γάρ).
I checked LfgrE (Lexikon des frühgriechischen Epos) on που. I don’t know what to think. They certainly thought that που often has a local meaning, including at Od. 1.161, 7.320 and 10.66. Of the passages with που discussed in this thread, the only one where they thought it was a modal particle was Il. 16.514!
Personnally, I think this is a bit arbitrary. As far as I understood the LfgrE article, they were not able to give any clear criteria as to which to meaning would apply in each case. I still think you may well be right.
I found an interesting passage where the meaning of που has actually some bearing on textual questions.
Od. 4.498 (The old man of the sea to Menelaus, concerning Odysseus):
εἷς δ’ ἔτι που ζωὸς κατερύκεται εὐρέϊ πόντῳ.
“One, I suppose, is still alive and is being held back on the wide sea.”
OR
“One is still alive and is being held back somewhere on the wide sea.”
A bit later, Menalaus asks the Old man of the sea (551ff.):
τούτους μὲν δὴ οἶδα· σὺ δὲ τρίτον ἄνδρ’ ὀνόμαζε,
ὅς τις ἔτι ζωὸς κατερύκεται εὐρέϊ πόντῳ
ἠὲ θανών· ἐθέλω δὲ καὶ ἀχνύμενός περ ἀκοῦσαι> .
“Now I know those. Tell me now who the third one is, the one who’s still alive and is being held back on the wide sea, or is perhaps dead. I want to hear it though I’m sad.”
Line 553 (underlined) is bracketed in many editions, but not the OCT or van Thiel. S. West says that the line was athetized by scholia, and she notes that “Proteus made it quite clear at 498 that the third leader was not dead but marooned. The line appears to result from a craving for antithesis, whether the poet’s or another’s.”
But thing is, I think, that “Proteus makes it quite clear” only if που on line 498 means “somewhere”. If it’s a modal particle, “I suppose”, then Proteus actually leaves some doubt as to whether Odysseus still lives or not. In that case, if 553 is an interpolation, the interpolator understood that που differently than the original author.