Good day all, hoping to get advice and opinions on whether or not to replace my existing central AC system.

A little background:

I live in Ottawa, ON - cooling season is about 3-4 months, where it can get up to nice humid 35-40C (95-105F) for weeks at a time.

We moved into a new place last November, about 1100sf. Current unit is a Lennox 10ACB18, installed 1998. It didn't start up right away this spring (~May 2012 - tripped a breaker), so we had an HVAC technician come out. There was a note on the unit outside indicating that there was "super seal" (probably one of these products: put in Sep 2011. The miracle touch of the technician being there made the unit start up fine without any breakers blowing, but he did recommend that we start shopping around for a new unit.

He also mentioned that there is a (higher?) risk of ice build up, and if it built up on the coil inside the furnace it could lead to additional damage there. He recommended keeping the blower motor on all the time as that would hopefully blow the water away from the internals of the furnace until we noticed the ice build up.

The unit ran fine all summer without any further issues (and no ice build up ever).

It's fall now, I've gotten several quotes with seasonal deals/rebates on all of them, but it's hard to justify spending that much money to replace something that has worked fine and a new, more efficient one will probably only save me about ~$30 / year in electricity costs (by my back of the envelope calculations).

So, with all that, 3 questions I would appreciate any feedback on:

1) Is there really a much higher risk of ice build up inside the furnace, and what kind of damage could that possibly cause? Could it completely ruin the furnace, or just some small repairs?

2) Based on the details here, would you recommend replacing now? Do you think it will last many more years with super seal in it? My main concerns with waiting until it dies are: not likely to get any rebates and it will likely happen at the height of summer, so we could be waiting a few days to weeks to get the job done.

3) If I were to get it done now, are there any recommendations of which make/model to go with, out of the following:
a) 2t York YCJF24S41S1
b) 1.5t Lennox XC13-08
c) 1.5t Lennox XC14-018
d) 1.5t Trane XR15
e) 1.5t Amana ASX14

From what I can dig up on the contractors, I like the one selling the York unit the best. It's an older, local company with excellent BBB record.

The other sales guys said things that didn't jive with things I had heard elsewhere which reduced their credibility (IMO) - were either of them on the right track with the following?: The Lennox guy said that the refrigerant hose between furnace and outside unit is "too short" and they would leave a 'loop' in it. The Trane/Amana guy said it wasn't a good idea to have the furnace drain straight into the basement floor, whereas the York guy said that was preferred.

Furnace is York, installed 2004 and still under warranty by the same company that gave the york AC quote (so there shouldn't be any he said/she said if there were any issues).

Sorry for the long post, I figured the more details the better. Any thoughts and opinions are welcome!