Hi Dionusius,
Welcome to Textkit!
I am not sure what you mean by ‘illusion’. I suppose it refers to the apparent abstract suffixes you mention in the prior paragraph. There is little doubt that οἰκέω is, as you say, denominative from οἶκος. But there is also little doubt that the -ία suffix in οἰκία is indeed an ‘abstract noun-forming suffix’. In fact, this suffix was especially productive in exactly this case: o-stem substantives and their denominative verbs in -έω.
The most recent work I’ve checked on this (Beekes, “Comparative Indo-European Linguistics”) suggests that the root meaning is not ‘clan’, but the ‘seat’ or ‘place’ of a tribe, family, or clan (as you say, vicus → vicinity). But there are reasonable differences of opinion about which of these meanings came first. Moreover, one can readily see how quickly notions of ‘clan’ and ‘the dwelling place of a clan’ could intermingle.
Although hardly decisive in such an argument, it is interesting that in its earliest known occurences οἶκος appears in the accusative with the allative suffix -δε (motion towards a place). Specifically, the Linear B Theban tablet Of 36, which is concerned with the dispatching of wool to persons and places, refers to ‘po-ti-ni-ja wo-ko-de’. This is rendered πότνια Vοικόνδε, ‘to the house of the lady’.
Cordially,
Paul
P.S. - You might want to check out http://discourse.textkit.com/t/representing-greek-font-notes-for-new-users/131/1 and start using the SPIONIC font. Your diacritically marked characters in the Unicode Extended Greek range are showing up as box glyphs. Private message me if you have questions about this.