1. Who uses flamers any more? I've only ever had to deal with Breath of Chaos from Chaos Daemons armies, and Doom Sirens from Chaos Marine armies. Never flamers. If your opponent is using flamers, they don't have melta or plasma guns, and therefore you should be a happy camper, even if your Reavers die.
2. The Heat Lances and Blasters are never worth it, and neither are Arena Champs or any of those upgrades. The real money is in the Cluster Caltrops. You get more attacks at much higher strength, making your Reavers a much higher threat.
The main reason that Heat Lances and Blasters aren't worth it is simple; you have to sit still to fire them (relatively. You have to not turbo-boost) so save the points and add some anti-vehicle to another squad, and do nothing but turbo-boost across the field, even if you have nothing to attack.