Anchor text is key, however the number of quality links pointing to you counts a lot as well. Rather than go back and change all your old tags, and links I advice you to look for new link partners and rather than go out on a limb getting links put together a plan working out how many links you want and how you plan to get them. Keep a spreadsheet of where everything stands and then go after your goal.
Going back on old links will be a nightmare and disheartning as several webmasters will not do what they promise to do and only half your links if lucky will be updated, and valuable time would of been lost.