Based on my playing with Gorn (and Roms) I would not go changing phasers to be less effective against plasma. Closing to range is 'interesting' but once they are there they are brutal. Any change you make has to account for what happens when you get close, halving phasers would make them nigh on unbeatable.
As Matt said, phasers may look nasty against plasma, but in the source games plasma will be out run to some extent even when launched from up close, so that it is weakened when it does hit. Full strength phasers is a reasonable reflection of the fact that you don't get to do that in this game - it is an 'averageing of all defenses' as he put it.
Take the AAR noted earlier.
Shooting 60+ plasma dice against a 9 ship fleet and seeing 45+ phasers hit it is a statistical anomaly, 7 out 9 ships getting IDF happens only about 2% of the time, then going on to hit with pretty much every phaser (including PH2s and 3s) is even less likely. You are more likely to see 3 or less ships get IDF (which will possibly be the ones targeted) than 7 or more get it.
Like it or not, plasma is by a long way the single most potent weapon in the game per volley. Even with phaser halving in the above situation, which is the best possible luck a defender could possibly dream of, you would have seen an extra 23+ dice (probably nearer 28 due to rounding) hit. That is an extra DN dead, or a couple of CLs.
In a more average case the defender sees say 4-5 ships get IDF, of which 2-3 are the ones picked on, the other ships contribute say 10 phasers (may be more or less depending on which ships they were and what they had in arc). The defender is maybe looking at only about 24-30 phasers all told to defend with, of which maybe only 20 hit (assuming some of those phasers are 2s and 3s). At the moment a 60+ strike (that Gorn fleet started with 76 dice) gets about 40+ dice hitting. If you halve the phasers that you get about 50+ dice hitting. Add in the Gorn/Rom phasers (which are in kill zone as well) and you are looking at a very toasted target.
Your heavy cruisers die to about 50-60 damage, or about 16 dice of plasma (devastating crits probably means it happens with a dice or 2 less). 40 dice will vaporise 2 CAs and leave another with no shields in a single turn. A few extra dice can take out 3 CAs in one swoop, halving the phasers makes that much more likely.
The main problem facing Gorns is NOT phasers shooting down the plasma, it is closing. But even there that challenge is mainly against Klingons/Kzinti with long range Drones and Disrupters. That, however, is lot easier if you are playing with terrain, which the game really seems to have been designed with in mind. It's even easier now drones have been pegged back. Despite their range, disrupters and drones generally struggle to do the necessary damage to prevent getting splattered by plasma when the Gorn do close. There were 76 plasma dice in the AAR Gorn fleet, even if they lost the CC/BC they still have over 60 dice left, which is capable of pulling back the game on one go.
The Klingon fleet from earlier in the thread only had 16 long range disrupters, or about 16 damage a turn beyond range 12. At range 15 they add in another 10 disrupters (another 10 damage beyond range 7.5). The drones they have (with the new drone rules) are little more than a nuisance, the most drones they hit a ship with is 8 at range 18 and less, and that leaves the second volley being no more than 5.
Not everyone is a klingon/Kzinti who can attempt to wear you down at range, Feds and the other plasma empire, or when they are brought in, Hydran and to a large extent Lyran are not good long range empires. ISC are mainly plasma, with a very nice long range PPD (but usually in limited numbers and a reload weapon), Vudar are Fed like, Andro are very lite on firepower but very tough and mobile.
