I estimate the value of an Alternator with 2 forms to be close to ((ideal/practical value of) form 1+(ideal/practical value of) form 2)/2 (Use the ideal values of the pieces if both forms are colorbound when separated but not colorbound if they become one & alternate) if the weaker form is just a strictly weaker version of the stronger form. E.g, an NW/N Alternator would be worth about (5+3)/2=4. For an Alternator where the moves of the 2 forms don't overlap, it'd gain some bonus. So, my Alacrious Alternator might be stronger than Fabulous FIDEs.
For pieces that promote upon capture, your opponent probably won't let that happen, so their value should be closer to their unpromoted form, while for pieces that demote upon capture, I estimate their value to be (value of undemoted form+value of demoted form)/2.
Armies with similar ideas:
I estimate the value of an Alternator with 2 forms to be close to ((ideal/practical value of) form 1+(ideal/practical value of) form 2)/2 (Use the ideal values of the pieces if both forms are colorbound when separated but not colorbound if they become one & alternate) if the weaker form is just a strictly weaker version of the stronger form. E.g, an NW/N Alternator would be worth about (5+3)/2=4. For an Alternator where the moves of the 2 forms don't overlap, it'd gain some bonus. So, my Alacrious Alternator might be stronger than Fabulous FIDEs.
For pieces that promote upon capture, your opponent probably won't let that happen, so their value should be closer to their unpromoted form, while for pieces that demote upon capture, I estimate their value to be (value of undemoted form+value of demoted form)/2.