Really, there's nothing you can directly do to speed up Illustrator. There is some unspoken, undocumented, limit and once you have so many objects that limit is passed, AI just gets horribly, horribly slow.
The slow down is generally due to screen redraw. So, if you can limit the need for the preview to redraw, things should be faster.
- Use Outline Mode when feasible (View > Outline Mode). Without the preview redrawing, Outline mode is generally "snappy" even on complex files.
- Structure your Layers so visibility can be turned off/on as needed. If you can hide a few layers, that should speed up screen redraw. However, you must construct files with this in mind (or copy/paste stuff to new layers later).
- Combine both of the above. If your file has a good layer structure you can place some layers on Outline Mode while leaving some layers in Preview Mode. If you hold down the Command/Ctrl key and click the visibility icon next to a layer in the Layers Panel, that layer will be put in Outline Mode. This can allow you work in Preview mode on a layer while seeing the structure of other layers without waiting for the other layers to preview.
- Use the Appearance Panel to hide or turn off visibility for any raster effects. Simply hide the effects while you work, then turn them on again to save/export the file.
- If you are using raster effects in the artwork, adjust the Document Raster Effects Setting (DRES) in the Effects menu. You can set the DRES to "screen" or a low PPI while you work. Then when ready for output, go back and set it correctly for the output (and wait for everything to redraw).
- Beyond these the only other thing you can do is to try and eliminate the number of actual objects by combining/merging objects when it's feasible. In My experience, it's never the amount of anchors that's an issue, it's the amount of actual objects.