TLDR : If possible, upgrade your RAM to 16GB and your CPU if your device allows it. I don't think the GPU would have a large a impact as these two components. However, any more recent system you purchase will probably perform better overall, thanks to advances in the tech which would come with the newer motherboard, faster RAM speeds and newer CPU technology.
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I have a Mac mini (late 2012) with a 2.5GHz i5-3210M CPU, 16GB RAM, Intel HD 4000 GPU. The CPU can boost to 3.1GHz when under load, and drops to around 1.5 GHz when not required.
I did a quick test, I made a dummy project, with one object and sprite, no code or events.
I placed 1000 of the object into the room.
I noticed when I select the object in the resource tree, and then hold down the ALT key and left-click within the room to place the object, there is a lag of about 3 seconds where the IDE locks up before control is returned and I can place another object using the ALT-mouse click method.
However, when I drag and drop the object from the resource tree into the room, there is no lag / lock up, and I can drag and drop another instance of the object into the room immediately.
I find this interesting, that two different methods of adding instance to the room, one is always immediate, the other lags, suggesting a difference in the way the two methods are coded, although the exact result is the same.
Also selecting an instance within the room, then using CTRL+C to copy it then CTRL + V to paste a copy into the room also has the 3 second lock up/lag of the IDE.
For another test, if I select a bunch of instances, starting around 200 or more, then dragging them around starts to get a bit laggy. But even if I select all 1000, while there is a little lag, its still usable, there's about a half a second lag between the mouse movement and updating the positions of the instances.
Repositioning a single instance (out of the 1000 in the room) by dragging it around the room there is no lag.
From this, I can tentatively say RAM is probably a small factor, CPU would be a slightly bigger factor in the overall performance. However, given my examples above, where one method has lag while the other does not, suggests something in the IDE code itself it not optimised for certain user interactions.
And finally, obviously any newer system, with a recent motherboard, CPU, RAM and GPU, all of which support a higher data throughput and processing speed, would perform better than upgrading any single component.
Even if upgrading your CPU, GPU and RAM was an option, they are still limited by the underlying technology incorporated in your motherboard, so that would still be a limiting factor.