Hm, this decision is probably too personal for someone else to answer. For what it's worth, there's a 7530 on eBay--bid starting @$650.
You'll need to decide if $500 to fix your machine is worthwhile to YOU. How much faith do you have in the repair person? Unfortunately, sometimes, even when machines are repaired, they can still have other parts fail. However, there are repaired machines that will run for another 15 years without any major problems. I'm just assuming (based on the cost), the problem with your machine involves a computer component which is a common issue with computerized machines. Like all computers, there are parts that will fail over time...that's just their nature. For the most part, computers will fail within 5-10 years. However, if they are installing a brand new computer component, it could be like a brand new machine.
On the other hand, you know your machine and you know what is wrong with it. Purchasing another used machine leaves you in the dark as far as whether the machine works properly, how it's been treated and serviced, if shipping is involved, will it be packed right and not arrive damaged, etc. Sometimes, just the comfort of knowing that makes your machine worth fixing.
If you contemplate replacing your machine, just sit down and make a list of all the options on your machine that you cannot live without. Then set out in search of machines that fill your list of must-haves. The price may help you make your decision.. Finding a new replacement machine could cost a couple thousand dollars.
Pfaff Creative 7530 Pre owned sewing machine
Thread What would you do Pfaff 7530