No reason to get new springs. Just get some air bags or Timbren bump stops (replaces the factory bump stops). I towed a 4k lb boat for several years with this setup and was very pleased.

http://timbren.com/

Well I just had to convert the RAS on my 2004 Limited due to system failure to coil springs and am having a set of air shocks made so I can control ride height under different towing situations. I am not a fan of air bags and there are currently no off the shelf air shock applications for gen4 4Runners. A1 suspension in Colorado is modding a set of Gabriel Highjackers for me but not cheap!!! $250 for the pair. I plan on rewiring/ plumbing the stock on board compressor with either a dash control or remote control to fill/ purge the air shocks. Back in the day I put air shocks on just about everything and I can't wait to get them in the 4Runner!

Oh yes, they will be going in at the same time with Rancho Quick Lift struts because I have to retrofit the XREAS system too! Why did I have to get a Limited with all options???????????????

I hope to end up with a more level tow anything go anywhere rig without the dreaded $$$$$$$$ repair bills and problems of the RAS / XREAS systems!