Stephane,
You can look also at LS7083/84, LS7183/84 (www.lsicsi.com). USDigial (www.usdigital.com) sells them for $3 q'ty 1. These chips are multiplying by 1,2 or 4. Using LS7083 gives you UpClk and DownClk, and you have to spent 2 counters for reading. LS7084 outputs clock and direction, so only Timer 2 will be used.
If you prefer to make the decoder in PLD, look at MIcrochip's AN532, you'll find pld code for the decoder with clock & direction output. Using bigger PLD, you can add some filtering of the input, if necessary.
Or, depend on your application, if it is acceptable to miss some pulses, just use channel A for interrupt and see channel B for rotation direction. That way you will count x1 only.
best regards,
Fedia