Sounds reasonable enough. If you haven't already done it, you might want to enable ignore-spm-downgrades in /etc/entropy/client.conf (see Re: how to make equo world ignore packages?
). Actually I usually don't bother with the procedure in your last sentence; I just install the newer version using Portage, although I don't see anything wrong with what you're doing.
Maybe I'm lucky, but I've had very little trouble to date mixing Portage and Entropy; I usually use the 'pretend' or 'ask' switches to keep an eye on what they want to change, before actually performing the operation for real.
Having the two package managers can be quite handy: sometimes I've broken something by installing a package using Portage and fixed the problem by re-installing it using Entropy (and, once or twice, vice versa).