I am an ordinary flight simmer who watches this forum quite regularly.
Does your Mac meet the minimum or recommended requirements? What do you mean that "its got all the original specs right now?" My research suggests it does not. About a third of the processor speed required. The X-Plane specifications can be found here at http://www.x-plane.com/kb/x-plane-11-system-requirements/ If it does not then don't waste your money on adding "external things" yet. One of the people who provided an answer in this link (experienced X-Plane user) has steered away from a laptop and definately from anything Mac.
If you need to purchase a new computer then go for a windows PC rather than an Apple (Mac) system. There are plenty of comments in this forum and by others outside this forum who would advise accordingly. They have a cooling problem. You will find the cost of a PC with plenty of "grunt" will cost you a lot less than what you will pay for a "mediocre" Mac.
Further more, a PC over a laptop will allow you to upgrade components individually over and above what a laptop does. Generally they are a "sealed" unit lacking space for internal expansion. One issue you need to consider is cooling for your computer. Some Mac models have poor cooling resulting in unannounced crashes whereas a PC will allow you to add cooling according to the area you live. You computer needs to run in an environment in the order of 25 degrees Centigrade.
Do you need a laptop? Have a look at the latest comments in this forum about using a new Mac laptop. The link is as follows at http://questions.x-plane.com/8398/what-kind-of-mac-laptop-runs-x-plane Your "new" laptop should have an absolute "minumum" screen size of 15 inch and a recommended size being 17 inch. Any thing else will give you diminished visuals.
Also have look at the answer provided by Rishi, a long term XP user in the following link http://questions.x-plane.com/8414/xplane-11-system-requirements
Alternative if you have to have a Mac (something Apple) scrap the idea of a new laptop or PC and download XP11 for an iPad. It is available from Laminar Research. I am not a Mac person so I can't comment on the reliability or performance and visuals.
What ever you decide to purchase and you want "good performance" use a Nvidia graphics card and an Intel processor. Avoid any other brands as some brands are poor performers. Don't waste money on a processor which has more that 4 cores (Quad core). It will give you no extra benefit as far as speed is concerned and allow X_plane to run faster. There are comments in this forum my Laminar Research staff advising a dedicated graphics card is required to run X-plane and not a graphics outlet combined with the motherboard.
Hope this helps