Guns and tanks are almost useless. Some are trading q5 tanks, and thats all. My suggestion is the first step to strategy: Guns get bonus while defending, Tank get bonus while attacking, Helies dont get bonuses. To attack with higher quality weapons, you must reach a certain strength and/or rank. Nice idea? Here is how it could work:

Suggestions:
-Helies remain basically untouched: 2.0 / 2.5 / 3.0 / 3.5 / 4.0
-Tanks and pistols get the following base bonuses: 1.0 / 1.5 / 2.0 / 2.5 / 3.0
-Tanks get an extra 0.5 while attacking (or oppressing a region)
-Pistols get an extra 0.5 while defending (or liberating a region)
-Tanks and Pistols get an extra 0.5 while not winning (or when the opponent is leading by (lets say) 400M damage)
-Tanks have an extra 50% base productivity (no raw cost change, so q5 factories at full bonus gives 45 tanks for 400 wrm)
-Pistols have an extra 100% base productivity (no raw cost change, so q5 factories at full bonus gives 60 tanks for 400 wrm)
-As the current companies can not match the changed rules, everybody is able to hit with q5 weapons, but their effect is the equivalent of the lower quality weapon one could use.

Examples:
-Defending and losing a region: q5 Pistol is 3.0+0.5+0.5=4.0, q5 tank is 3.5, q5 heli is 4.0
-Attacking and winning: q5 Pistol is 3.0, q5 tank is 3.5, q5 heli is 4.0
-While q5 helies cost 6g, q5 tanks will be around 4g (+50% productivity), and q5 pistols at 3g (+100%).

Effects:
-three different types of weapons in the battlefield and in our storage and on the market.
-three different types of weapon factories used
-five different quality weapons in demand
-the losing side gets bonus (as tanks and pistols will match the helies in certain cases, but will be cheaper to produce)
-the company tree gets sense
-the weak and usually defending nations/small communities get a advantage

+1 suggestion:
while defending with DS, Pistols get an extra 0.5



Other still shiny suggestions:
Save the game - Open letter to Biskvit
Why haven't yet implemented some powers to the members of the government?

Second step to strategy: Artillery. The offensive side may call to build Siege artillery. People can chose to build this instead of fighting. Every 'damage' they make without weapons cumulates for 8 hours. After that period, half the cumulated damage is dealt every hour (no need for halving, in case we could hit with our hand at -50% penalty at least). So 15 rounds at max can be done, 7.5 multiplier. However it can be damaged, ever since it is started, every damage the opponent does while winning (leading by 400M damage) damages the artillery itself instead of added to the wall. Thus it also can work as a defending wall at the end of the battle...