Its my understanding that the Mongoose is just a spyder clone..
My previous marker was a all mechanical spyder (and no eyes). The vibe is a step up from that, a small step, but better..
However, if your mongoose has an e-trigger and eyes, then you might actually want to shoot a Vibe to see for yourself if you think its better. In stock form the vibe doesn't have eyes, and is capped at 11bps.
I think an ION would be an upgrade to what you have. Out of the box it would shoot almost as fast as what you have now, but its much smoother, quietier and easier on paint than the blowbacks. The smoothness will really help your ball-on-ball accuracy, right out of the box.
Then, the ION has alot of upgrade potential which will greatly surpass what you have today.
hmm for 250 you have a lot of choices. For new, you can get an ion, a promaster, or a proto slg. those are within your budget and are an upgrade to what you have. In the used department, you can get a plethora of different markers. dm4 with ul frame, pm5 with ul frame less than 200 a lot of times. there are nerves, fusions, pmr, quests (if you are lucky for 250), upped ions, upped promasters, shocker sft (sometimes), 05 angel speed, freestyles, and the list goes on and on. Remeber that a year or 2 ago, these guns were considered the high end guns (except for fusion and pmr, mid end but still good guns). Does a year old or two year old (or 3 with dm4) make it a bad gun? If I were you, I would look at a nice used gun in the bst. GL with your search.