I don't think it was 'refusing to develop the story', more trying to balance the overall arc with a somewhat episodic format. There were some ideas that weren't expanded, but overall I think the storyline was strong and relatively coherent. Do you have any examples besides a feeling that the stories could have been more in depth?
Balancing the serialized and episodic elements is what prevented the writers from really developing the more intriguing plotlines. I don't mind an episodic story every now and then, but it shouldn't interfere with the important stuff.
Here are a few initial ideas for developing storylines to their fullest:
The Goa'uld - They were turned into jokes from the first, nothing more than flamboyant bwahaha baddies to serve as target practice for Our Heroes. I would have made far more effort to develop them as a coherent species, with enough depth to allow them to break out of their cardboard role.
They should have had more social cohesion so that they would be more impressive foes. It was far too easy to beat them by turning them against each other. I liked the notion that they were a reasonable, intelligent species that had been driven insane by collecting too many memories over too many lifetimes, so what's the solution? Perhaps an effort by their offspring to supplant the insane old folks and get them out of the picture?
And
were all of them insane? To give them more variety and depth, I would have depicted some of the older ones as being completely and irrevocably round the bend, but younger ones (Nirrti and Ba'al for instance) simply being cynical poseurs who affected Goa'uld looniness to keep the peasants in line.
The Tok'ra - A real lost opportunity. How and why did they behave differently from the Goa'uld? Why did they develop a separate ethical philosophy? Are they "sane" simply because they haven't been driven crazy by too many hosts' memories?
Regardless of their superior ethics, there's no getting around the inherent conflict between them and the Tau'ri, considering they cannot survive as a species without human hosts (something I don't think was ever absolutely clarified).
The series negated this interesting dramatic direction by having the Tok'ra have no queen and therefore no incentive to expand the worlds under their influence to accommodate her offspring. I wouldn't have short-circuited this storyline, I would have jumped right into it feet-first.
The Jaffa - They never really broke out of being Klingon knock-offs, but I would have pushed for better development. There was one episode that suggested the tricky Jaffa/Tau'ri/Tok'ra alliance could become interestingly problematic for all concerned. There's another plotline I would have jumped into feet-first.
Via this alliance, I would have had the Tok'ra gain so much power from their alliance with the Jaffa and Tau'ri that they were on the verge of supplanting one Goa'uld empire after another. Then the issue becomes: how much of an improvement is this, really? Are the Tau'ri simply building up the next threat down the line?
The Tau'ri - Having the Stargate program and its scary implications become public knowledge might be an unworkable storyline, since it would broaden the dramatics far beyond the confines of Cheyenne Mountain. But I never bought the idea of international cooperation as depicted in the series. There would have been a lot more jockeying for position and mistrust given the stakes.
The Rit'u - Their viewpoint was eminently sensible: if the Goa'uld are a problem, solve the problem by eradicating the Tau'ri. This element should definitely have been brought into the story for at least one season.
There are other elements I wouldn't have bothered with, such as the Ori, who never really stuck me as interesting. The Wraith are a whole other topic, but my ideas for them might be too parallel to the Goa'uld, so maybe they should be left on the cutting room floor as well.