How often is "quite often"? Pump seals, when used with the appropriate solvents and add-ons, the seals should last a long time. If you're using buffers they can salt-out on the seal, which reduces seal life, but this can be prevented using the seal-wash upgrade. Make sure you're using the right seals though - Agilent sells seals for reversed and normal phase. Also, are you sure it's the seals, and not the AIVs or the AIV cartridges or the outlet ball valves or the plungers that are the culprits in a leak situation, which at first glance might cause you to think the seals were leaking?
As for the lamps, you should get between 800 and 2000 hours (depending on lamp type) per lamp. So, two new HPLCs for $90 worth of seals and a $800 lamp every few months? Sounds like overkill to me. On the other hand, a service contract, even for an old 1100, is between 5-10k per year. A new LC, would be, (just guessing) $50k, ballpark? Maybe more? Just my two cents.
On the other hand, depending on the work you do, a UPLC from Agilent or Waters (or any of the other vendors who sell a "UPLC") might be able to do the work of both HPLCs (higher throughput, faster runtimes, etc). But remember, all instruments do have maintenance needs or service contract costs, so bear that in mind when budgeting for new equipment.
Oh, and until last year, my boss was still using 1090's for everyday LC/MS analysis, until his last one died. So, as long as they're maintained and you can get spare parts, you can use one of these instruments for a good long while.