I think the investment in a current style spawn point is still pretty worth it. Take for example a 5 mana cost no channeling spawn point. I know you said not to accept the suggested stats as set in stone, but they provide a worst case scenario for my argument, since I believe 5 mana and one full action is payed back rather quickly in terms of creature summoning.
A fair number of channeling spawn points run close to 14 mana, but have additional means of generating mana. This brings their effective channeling above 1 mana a turn for most circumstances. A spawn point without additional mana conditions runs closer to 10 mana casting cost. This means that the proposed conjuration would leave you short 5 mana relative to a channeling spawn point without mana conditions, and 9 mana compared to one with conditional extra mana sources.
5 turns after casting, the channeling spawn point has payed for itself, and the mana conditional spawn point, in many cases, will have done so as well. Obviously, you have less mana leading up to this point, and more mana afterwards, but very few games seem to last fewer than 6 turns, at least for my group.