Hello Que,

Just jumping on the different discussions to add my comment:
- value: it is hard to answer as this may change drasticaly depending on were you are, when you buy it and lastly how deeply you look for a piece. Some helmets may be very rare but unwanted so with little value. I would myself not be very confortable in providing any price. Some sellers or forum may instead provide good trends.
- concerning the identitification, the forum is of course a good source of information and with plenty of collectors that would be happy to help. (I responded to your posts). That of course do not prevent from doing its homework and seek for information. Some helmets may be difficult to identify but some, like the Adrian M15 are very commonly represented for WW1. That also help those who will help you focus on what matters instead of having to reexplain the full story from scratch for each helmets.

I hope this help

All the best