Wide format Print

When I do billboards or signage I set up my art (raster) @ 600dpi - with the artboard equaling 1" per each 1' of finished art.

All text should be vector not raster at min 1200 - 1400dpi (I believe 1400 is AI default).

Why? A good large-scale print house will have better image enlarging sftware than most designers. If I give them 600dpi ft/in - they have a nice high res image to start with.

You probably don't need to send a full size PDF to your printer, half size or quarter size is common in wide format.

As has been stated above, keep your image elements vector when possible, as vector objects can be enlarged or reduced without loss of sharpness.

Your raster effect settings need to be set corectly, 300 ppi as the final effective resolution is standard, but for wide format, lower is often fine, as the poster will probably be viewed from a greater distance, check with your printer. You can preserve the vectors by placing your Illustrator file in InDesign, enlarging and exporting to a new PDF (with bleed), or you can make your Illustrator file the correct (reduced) size and save as a PDF. Your placed images will need to have sufficient resolution to maintain sharpness at the final output size.

You can resize images in Photoshop and add a bit of additional sharpening, before placing into Illustrator, if needed.

A couple of things here:

1) You need to realize that while Adobe Illustrator is a vector-illustration program, it widely applies raster effects to your vector drawings. Stylizing effects like drop shadows, bevel and emboss, etc. are applied the same way as they are in Photoshop — by "painting" in soft transitions with pixel-based information. There are also other areas — like some gradient effects, placed art, etc. where raster effects can come back to bite you. You need to account for that raster effect information when you trnasition into creating rasterized output for your Illustrator file.

2) When you create rasterized art, you need to account for your effective resolution needs for the final output size, and take that into the account from the beginning of the process.

Both of these factors may be affecting your scaling issues when you create your rasterized art. Let's deal first with your raster effects. Before you rasterize your art, you need to ensure that you're getting sufficient effects resolution inside your existing vector art.

By default the Document Raster Effects Settings options box, which you access through the Effect>Document Raster Effect Settings... menu command, gives you three standard settings for your raster effects output — Screen, Medium and High, as shown below. There's also an option for dialing in an Other resolution:

As we discussed earlier, since image resolution is fixed when you create rasterized information, you need to account for needed effective resolution at the final reproduction size. I'm going to make an assumption that your 7' x 8' final graphic is being created with large-format printers for signage/banners. So I'm going to shoot for a final effective resolution of 75 pixels per inch (ppi) for two reasons: one is that this is a common specification for this kind of work; the other is that using that number makes the math easier.

We need to dial in a custom number for our effects, since we're scaling up twelve times the original size of the art. Since we need an effective resolution of 75 ppi for final reproduction size, and were scaling up 12 times, the math translates to 75 x 12, or resolution of 900 ppi.

If we have any raster effects whatsoever, we need to first scale up the resolution of the effects to preclude rude surprises when we rasterize the art for final use. Otherwise, you'll get great results with the right settings for all your rasterized vector art, but your effects will be hopelessly messed up.

Now let's address your rasterizing problem directly. Rasterizing at 300 ppi and blowing up the art 12 times gives you a final effective resolution of 300 ÷ 12, or 25 ppi. That appears, as you report, as really blurry in Photoshop and if you try to print that out, it'll give you a linescreen value coarse enough to sand a hangnail down. When you rasterize the job, you can either manually dial in the correct Other resolution at final reproduction size (75 lpi x 12, or 900 ppi), or you can use the correct Document Raster Effects settings we've already dialed into this job.

This should get you the results you're looking for. But before you go further, check with who will be producing your job to get their desired specifications, and apply these factors to come up with precisely the resolution you need for your job.

Hope this helps,

Randy

Absolutely do not export it as TIFF JPEG or PNG. Absolutely do not take it into Photoshop.

If you find this advice hard to follow, please say WHY you are doing this strange thing with your vectors. 

If you want to print from Photoshop at a high resolution, you would want 300 dpi at your target size of 7 feet x 8 feet (84 inches x 96 inches). I would suggest that you place your Illustrator file as a smart object into a Photoshop file that is set to your target resolution.