The method I used for enlargement was: Image size -> resample - bicubic smoother (best for enlargement) - in three steps, 200% up - 200% up - 150% up.
Why did you do that?
Incremental upsizing in Photoshop is an obsolete technique.
For products that size about 72ppi usually suffices in my experience.
Has the printer expressly demanded 300ppi effective resolution?
Yes, the specs I got from the printer says 300 dpi. I totally agree with you that 300 is a bit overkill on prints this size, considering the viewing distance.
I have no good reason for doing what I did, just trying out stuff. I did however end up with a better image, compared to the enlargement done within InDesign.
What would be the best way to enlarge this image, if the printer accepts 72 dpi resolution? The original image is 300 dpi.
When you "viewed at 100%" and the "image looked ****" to you, was it just fuzzy or was it pixelated (visibly made up of colored squares)?
If the former (fuzzy) is what you saw, your only recourse to not have it "look ****" is to either start with a higher resolution image or to use a more sophisticated upsampling technique, such as provided by OnOne Software's Perfect Resize 7 or Alien Skin's Blow Up 3.
If it's pixelated by the resize option in InDesign, are you sure there are no options there that will do an interpolated (e.g., Bicubic) upsample instead of a pixelated (Nearest Neighbor) resize?
Did you TRY printing a small portion of the image (e.g., on your local inkjet) to see how the print would actually look?
I do not contest that upsampling in Photoshop gets better results, but I’d just do it in one step and then maybe sharpen the image (and possibly add some noise).
I use Perfect Resize a lot and it works well. 8x should be doable but sucess will depend on original image quality, subject matter and practical considerations like viewing distance...