Pete,
Don't forget you can trade traffic without blind-links. A little "check out my friends" table will do pretty well in a good spot. Also if you're trading with UCJ sites you can get a good return because your traffic will be productive. I usually get more than 150% back from good UCJ sites like Snaggleporn. That way you can get the best of both worlds.
xApster said you need to keep some fresh traffic coming in and he's right about that. I have a lot of bookmarkers, I get quite a bit of SE traffic and some clicks from recips - but if i ever want to double the bookmarkers I've got to get some exposure to new surfers.
If I trade 400 to Snag then get 600 back, and only 10% like my site enough to bookmark - that's 60 people added to "my traffic" a day. I'd hope that more than 10% likes my site, but even if they don't 60 a day will add up to 1800 "new regulars" in a month. Then if I also trade with 4 other sites, it builds up.
Find some sites and trade some and see how it goes. Come to my site and trade, if you decide you don't like it my feelings won't be hurt.
www.adultcore.com