I got pet insurance last year shortly after my dog came down with pneumonia which cost me nearly a thousand dollars to treat between vet costs, x-rays, medication, etc. If I had the insurance prior to the pneumonia, treatment would have been incredibly less expensive, even including insurance costs. Beyond that, it also gives me peace of mind knowing that I don't need to worry about paying for my dog's health care if something were to happen.
Case in point: yesterday I came home from work to find that my little rascal decided to have a snack of trail mix (with raisins in it) while I was out. I didn't have to worry about whether or not I could afford taking her to an emergency clinic-- I was able to just take her, knowing that once I'd paid the deductible, the insurance company would cover 90% of any hospitalization time, tests, and treatments needed. (Though, I haven't put in the claim yet, so my feelings could of course change if it's rejected
If you decide to get insurance, make sure to carefully check what exactly they cover. Not all companies cover shots, so if that was something you wanted covered, make sure that the company includes it.
Additionally, as BrittaS said, if you choose to get insurance, you may want to wait to take your dog in to the vet for the bumps. (Only, of course, if you feel this is something that isn't urgent.) As she said, if it's detected prior to applying for the insurance, they'll likely deem it a preexisting condition and will refuse to cover anything they consider related to it. Also check if the plan you decide to get has a waiting period. If they do, any conditions detected or symptoms noted during this time period would also be considered preexisting conditions or signs of a preexisting condition, even if you already have a plan.