You seem to be inclined to keep the old bike, which is good. On paper the Insight looks good, especially for it's price. I would not recommend lowering the front tire pressure too far lest you suffer a pinch flat. Depending on your body weight, however, you may be able to lower it substantially and still remain safe. Check out this little calculator to estimate tire pressures that you need for front and rear:
http://www.dorkypantsr.us/bike-tire-...alculator.html. You're right that an aluminum frameset could translate into a rougher ride, but IMO this is something that you could adjust to. You can learn to stand up out of the saddle (even slightly) when going over bumps, and to keep a light grip on the bars with your elbows bent. Another option is to install fatter tires (if they'll fit). That being said I weigh nearly 300 lbs. and I find that my 32mm tires are just fine.