1D vs. 1Ds Mark1's for second 'play' camera

Long story short, I been shooting with a 60D since it came out and have been very happy with it as a day to day shooter. Recently though, I've been playing with the idea of getting a used second body that has a sensor larger than APS-C. Mainly to experiment with the wider effective field of view and DOF on my expanding lens collection. For example, I would like to shoot wider with my recently acquired 24mm TS-E. Also wouldn't mind having a second used body I wouldn't be as afraid of wearing out on time lapse or long exposure photography or use in less than perfect weather.(for reference, I've found the auto-focus starts to fail on a Rebel at around -25F)

Now the question. I've been looking at getting either a used 1D mark1 or 1Ds mark1. Haven't had the oportunity to shoot with a larger sensor camera outside of playing with a 5D mark2 in store. Curious as to actually how much of a difference there is between a FF sensor and a APS-H. Coming from a APS-C, how much of a difference will I see shooting with a 1.3x magnification vs. FF. Since I am just an advanced hobbiest, price is a factor. From looknig around, a 1D can be had for around half that of a 1Ds. Is the added benefit of FF over APS-H worth that price jump. Also looked at maybe a 5D mark1, but the different form factor of the 1D series looks interesting.

So for those that have shot both, what are your opinions and advice? Any help would be appreciated. Thanks.