Unfortunately, there are no bios in the horizon for TP, no. As of this writing at least :-). There hasn't been anything major written on him, if I'm not mistaken other than the odd article here and there. Jeanine Basinger's recent book contains some of the 1st (serious) work written on Power for several years now.
As for the Arce book, yes, one has to wonder as to its scolarly value. The fact that there are no footnotes for his sources or even an index for that matter, makes his research a bit suspect. Still, it's the only book out there that discussed TP's bisexuality and it looks like it may be it for a while as well--however accurate or not.
The author of the Last Idol is on a more academic track, and far more detailed oriented, if memory serves, however it follows more of a mainstream path than the Arce book.
Here is a link, for starters, that sites some other reading sources regarding this subject--scroll down to "post-death rumors": http://www.answers.com/topic/tyrone-power
Perhaps someone else here can come up with more thorough info.(?)