1) I do not discount the need for planning keyword density, well-designed meta-tags, and similar on-site tactics. You should make sure all of those things are done right. However, I believe that in the scheme of things, the weighting that search engines put on these elements is decreasing rapidly, and will continue to do so for the forseeable future. That is why I would be wary of an SEO consultant that focused on these items and tried to make you believe that their rewriting of your metatags is likely to make a big difference in your rankings.
2) Inbound links are important. However, my philosophy is very simple. Instead of coming up with strategies to trade for links, buy links, etc., you should focus on offering something that will make people want to link to you. I may be wrong, but I am guessing that search engines will soon be able to discern between sites that have artificially generated links and sites that naturally generate links on their own.
3) I do not claim that it is illegitimate to try to build sites with gimmicks and tricks that will rank well in today’s search engine world. If it helps your cashflow, go for it. However, I would be wary about doing that kind of strategy with sites that you really want to be there long-term.
4) In the past, you could quickly throw up microsites and easily get rankings. That is changing rapidly. I believe that you will have better success by limiting the sites in your portfolio so that you are not spreading your SEO resources too thin. In the future, I expect that the resources needed to get good rankings will continue to grow and this belief will become even more true.
5) The time needed to implement a solid SEO strategy is growing. You might need to plan on years before recouping your investment in many industries. As mentioned before, if you can use crash and burn tactics on throw-away sites to get quick cashflow, go for it.