From my point of view, for a small sailboat or cruiser heavier is better, so long as it is low in the boat. I don't know how much heavier meranti is than okume, and so far have not been able to find out, but if it is significantly heavier then it could be a boon to use it in the keel and lower hull panels (as long as you are able to bend those lower panels properly when using the denser meranti -- wet, hot towels are a huge help). Anyway, in my limited experience, weight low on the boat and wood stiffness add a lot to the stability and handling of the boat. Use okume higher up--it is lighter and often has a smoother finish.
One caution I have read about, not all merantis are the same. Be sure it is 5 ply BS1088 marine meranti, and supposedly the best brand is Hydrotek.
All that being said, the folks at CLC have done a lot of research on this and have many combined years of experience. I think you can rely on their judgement--more spent now could save you a ton of money in the future. You can find a lot of horror stories on this forum by people who have used inferior materials. This is especially so in the keel, centerboard and centerboard trunk, and lower hull panels. It is difficult if not impossible to effect repairs to the keel and CB trunk. Take a look at the threads in the Forum Posts: "How is this possible, and how can I fix it?!" and "Centerboard of Doom!."
Another good source of information on this is Sam Devlin of "Devlin Designing Boat Building"
http://devlinboat.com/, although his opinions sometimes vary from those at CLC.