I'll try and answer the OPs questions. These are all just my opinions, so take them for what it's worth. Let's see...
I
suppose the title says it all - does the suggestion of sex sell poor
video games?
Yes. It does. Look at games like Juiced, various other "underground" racing games, and most 3D fighters. Innuendo and suggestion is a very big part of marketing. At my GameStop there's a floor mat with a woman who is larger on the mat than the title of the game.
Is it a good marketing tactic?
Well, it does help, but in the end if the game stinks, sales will slowly drop off once word gets out. That and your credibility will start to go down with others (in my opinion) by stooping to tactics like this to sell an otherwise poor game.
Are games that would
otherwise be really boring sold by some fairly poor looking
representations of the female form barely clothed?
Pretty much same as the first question.
Is it a good idea
and would it be recommended as a marketing strategy especially to get
published?
If you are the developer seeking a publisher, it is not really your job to do any marketing. You just make the game and pitch the game. They will handle the promotion and marketing.
Also, is more realistic better - if I included models that
had almost photo realistic high definition females would that be even
more likely to sell?
That depends. Sometimes attempts at photorealism leave people feeling more awkward about it than anything. When you get real close to realism, but fall just a hair short, it's almost worst than not going for photorealism. As far as the relationship to sales numbers, it's pretty hard to say.
Do females in the role of the action
hero partially clothed create a response in the player that makes them
want to play and ignore other elements of the game?
With some people, sure. Most gamers though will stop playing the game, then word will travel of the poor quality of the title, and then sales will decline.
Overall, I believe that using sexual content of any nature to promote or sell a video game is terrible. I frown upon any company that does this. It seems very cheap when the makers (or publishers more often) have such little faith in the selling power of the gameplay that they try to get people using suggestive images. If you are making a game, don't aim to sell this way, just make your game good so people will want to play it.