Hi all, I'm new to this forum and appreciate any advice on the topic of insulation.

I have a 24-25 year old house. It's a modular (24'x48') with an addition. My question is about the (original) insulation in my attic.

Looking at the pink fiberglass roll-out style of insulation, it's appears that there's 2 layers of approx 6" each, making ~12" of thickness. But there's not 'paper' on either side to note the make/model/R value of it. I'm assuming it will compress over time, so it may have been thicker when new.

In my opinion, my house is relatively well insulated, as we don't feel any drafts nor does the heat (1.5 year old natural efficient gas fired furnace w/hot water baseboard). When the addition was being added 2 years ago, I took off all the trim around windows & doors and used the spray foam (Great Stuff) insulation.

I've kept track of the heating bills for the past 5 years and with the new furnace, keeping our heat between 62-65 degrees (previous years 66-69), and foam insulation in windows & doors, we've cut our amount of natural gas usage by ~50% (which included adding 50% more living area to heat).

I'm concerned with the old original attic insulation. I'm not sure of the life of fiberglass and how much it deteriorates. If there's a benefit, I'd like to replace it with better (blow-in?) insulation, but I want to get decent bang for the buck. I know the spray-in foam is pretty good (tight seals & high r-value), but I don't want to pay an arm/leg for it and my return on investment may take 10+ years. (I may be moving in ~5 or so).

For those of you wondering, my highest monthly gas bill in the winter has been $215 (for 172 ccf's) since the new furnace was installed. That usage includes the clothes dryer & oven (both powered by gas).

My questions:
Is my current attic insulation old enough to replace?
What would be a cost effective option to replace with (higher r-value fiberglass, spray in cellulose, spray in foam)?

Thanks,
Warren