If you want your existing Solitaire to have maximum light output, then buy the LED and glass window upgrade.
If you don't have a Solitaire and buy the Fenix, then you will be missing out. Why not buy both the Solitaire and Fenix then buy the upgrades... simple.
No need to compare if one is brighter/better then the other to make your purchase justification. How many of us here have only one Flashlight? If we based our buying on price to light ratio... then we would have only one Flashlight (your choice). That is not the case here for CPF/MP members.
So buy both Flashlights and be sure to buy the LED and glass window, from me, if you want maximum light from your Solitaire.
Njoy...