There are a few things you could do. ( NOT that I recommend you do that )

1. Use a plugin that cuts of the title after roughly 69 characters ( http://wordpress.org/plugins/limit-a-post-title-to-x-characters/ )

2. You could eliminate the Brand Name in the Title .. if its automatically appended ( perhaps that is what causes the title to go over 70 characters )

BUT what I would recommend is export out the list of pages that has title over 70 characters  and write proper  titles for them, its the best option BUT as you can imagine its not going to an easy task. I guess NO Pain NO Gain resonates well here. I would do this for the important pages first and slowly work at them over time.

If you are sending Facebook and Twitter Trafic to these pages try and use Facebook OpenGraph and Twitter Cards

I am sure if you searched for " ~images -images" before Google decided to drop the ~ operator , pictures would have come up as an alternate keyword and so, they would have seen it as a close match for pictures and served your site for your query.

It was one of my fav tool for finding alternate keywords to optimise for , sadly that is gone now

As for on page vs off page both are important .. it not an "either or" condition you should do both to get good results , especially if the competition is strong.

Personally I would index comments but have a nofollow attribute to links within the comments. See what sort of tile and description the comments url generate ( you dont want duplicate titles and meta for those )

EDIT:

do you have some sample urls we can look at ?

When it comes to subdomain vs subfolder, SEO's usually prefer to go subfolder. But if it's easy and financially suitable to go that way I would say go for subfolder. In this day and age the SEO impact is minute ( if any )

Matt Cutts's view ( Oct 2012 ) : http://www.youtube.com/watch?feature=player_embedded&v=_MswMYk05tk