I thought the show was obviously trying to make the guide out to be annoying intentionally. As for SG-1 not being her fave...maybe she has the hots for someone on one of the other teams
.
As for the gate defenses, I though they were rather simplistical,too. But if I could explain them away..rather poorly...maybe because of the extensive use of the gate they couldn't be overbearing in the defenses (like airline travel...we could have better defenses against terrorists but I dont think people would go for strip searches at the security checkpoints
). And the threat of terrorist attack might be less in 2010 so they might have not felt that a strong defense was necessary. Historically,most defenses are a response to a previous attack against a target and they may not have had an actual attack against the new Stargate port in DC.
As far as defending against incursions from the gate...The Gou'ald are dead...the snake menance is gone..eat,drink,be merry for the universe is ours...
Basically, the politicians have probably felt that there was only one real threat and now thats gone and any other possible threat (and the pols probably dont believe that there is one..at least their re-election promised safety and prosperity forever because of their leadership over the last few years) can be taken care off by earth military and Ashen tech after any alien beachhead is established. They thought it in 1914 and in 1938 so why not in 2010.
As for Sam's choice in husbands...my imagination doesn't reach that far.
As for Janet...the big plus for me is she appears to be still single and has plenty of free time for dating in the future.
The timeline issue....maybe the future of 1969 depended on the events of 2010...The timeline may not be a straight line but goes in zigzags...like going to leave the first room and going into a second room to get the keys to the door of the third room leading back in the first room...
The series has showed that alt.universes exist but the technology used to get their appears to be different from the gate tech (at least the device used is not part of the gate but a separate artifact). It can be argued that the gate operates solely within one universe but the mirror uses different physics to breach the walls between other universes. Therefore, the use of the gate to travel time is actually affecting their own timeline and not creating a new one. However, there maybe a timeline where they never used the gate,where Janet never offered to give Sam a checkup or even one where Sam was killed before she could get the paper through the gate. But the show is about SG-1 and their(our)timeline not another SG-1 in another timeline (where they die in Cheyenne Mt. fight Jaffa troops lead by First Prime,Teal'c or retire and open a Mcdonald's franchise on the Una's homeworld serving Goa'uld On A Stick in a special sauce).