They won't lower or rid the filibuster. Why? As much as they'd like to get what they want, they know that when the other side has control, similar to what happened in 2005, they still want the filibuster available to them. This exact thing was discussed at that time as well, but with the roles reversed and obviously it being on talk radio instead of the lamestream media. The wallbanger and golfer talked about ridding the filibuster, but itch reminded them that in 1993, it was needed.
Think of this more strategically. I don't remember the last time the GOP had over 55 Senators. Even in the heyday of the Gingrich era that was their ceiling and it included some pretty liberal Yankee Republicans (Chafee, Jeffords, Snowe, Collins) to make up that majority. During Bush II's time I think they hit 53 maybe.
So, if you set it at 55, and then look out over the next 4 years, what chances are there that the Dems will be in the minority and be under 45 seats? Even if they lose all 6 seats at risk next time (WVA,LA,AR,AK,SD,NC) and don't get any back (Collins doesn't retire) they're still at 49 thus preserving filibuster power and then 2016 swings back to them anyway.
Tactically it makes sense. Gaining 56 Senate seats would be a historic achievment given the strong unpopularity of the Republican brand, plus the presence of a lot of Republican Senators in Dem states (NV, IL, NH, PA, WI, IA). Personally its a chance I'd take.