Getting a visor doesn't guarantee that you will have all those bonuses. Standart visors will grant you increased accuracy, only those really, really good one will give you some bonus to LOS (1 I think is absolutely enough) or infravision (reduced intuition over +2 of LOS ).
No. Just - no. Why ? Because
Two slots is really overdoing it.
We have armour, boots, a weapon a secondary weapon and the new helmet slot. There is no need for a very specialized slot. The whole point of roguelike items is that they should be as diverse and random as possible, with many not-so-overpowered options.
The real questions is: what can we put in the 'helmet' slot ? We need to think of the spectrum of possible effects and names...
Here's my list of ideas (of course - the bigger the benefits, the harder to find the items are. Also - some combinations can be used to create unique headgear :>):
1* +1 or even +2 to armour
2* +1 or +2 to LOS (We could make +1 helmets quite common... and lower the defaut LOS of the player by 1 ]:>)
3* 10%-25% more XP from kills
4* Dilated Perception: higher fire / reload speed and/or chance do dodge
We could even have some activated abilities (with a limited numer of charges) you would use by pressing the fire button while in "look mode".
For example -
5*a scanner (AKA - portable computer map),
6* heat/motion detector (shows monsters within a specific radius regardless of walls),
7* perhaps some chemical stimulants (AKA portable berserk - could be shorter then normal and, once again, with limited charges),
8* painkillers (portable healing)...
9* OK - THIS is something awesome... A portable force-field generator! Makes you invunerable for 2-5 turns but also makes you IMMOBILE. Either completely (meaning that you can't do anything but wait) or allowing you to use items but not shoot anything. It would be great for healing during the heat of battle but most of all - it would allow you to survive a nuke blast.
Of course - you could just make the force field disappear EITHER after a certain period of time OR after it suffers sufficient damage (meaning a monster could shread your sanctum beforethe nuke would go off).
10* Of course - the helmet could have a built-in phase device (hell - some might even come with an unlimited numer of charges and simply with a time limit between them). Not a homing one, of course...
11* Remote control - the ability to pull levers from a distance (which makes me wonder - do we get the XP from monsters dying of lava/acid into which we shoved them ? We should, IMO.)
12* Telekinesis - the ability to push monsters / barrels / items from a distance... (Come to think of it - we might even have a "Telekinetic" trait...)
Of course - if there was more than one look-mode ability available at the same time, you could cycle (of course - without any turns passing) through them with the "swap weapon" or even "reload" button.