My Situation: I have a real world object, part of a motor vehicle, made of plastic, which has degraded and no longer available to purchase.  The owner wants me to reproduce it using 3D Print.
My workflow:

1. Import JPG into Inkscape,

2. convert to SVG using trace function,

3 save the SVG file.

4. Insert the SVG file into Fusion 360, it creates a sketch,

5. I can then trace over the shaoe (repairing broken defects in the model)  to model the exact shape in 2D,

6. convert to 3D solid object using extrude function in Fusion 360.

The process fails at step 4.  Fusion 360 hangs.  I think it is because the SVG file contains too many small objects, several hundred thousand. I need to somehow simplify the svg file so that Fusion 360 can handle it. When I import the svg file, it appears on the sketch plane, and I can see that it has not only traced the basic shape of the item, but also included a lt of fractal type lines around the outside and inside of the basic shape of the model.  I think I need to alter the threshold between colors/brightness steps to minimise these artefacts.  How can I do that in Inkscape ?

Path>Simplify may help.

There may be other avenues. Feel free to share the jpg and the SVG, by attaching to a message.

Thank you @Tyler for responding so quickly.

I have found that by selecting "brightness Cutoff" option in "Trace Bitmap" that I can reduce the number of cloud points in the output image down to 15500 or so, and Fusion 360 can handle that. I do not need the colour of the object for my purpose.
I am not sure where I might find the "simplify" option, are you referring to F360 or Inkscape ? 
If it is F360, the failure occurs at the point of inserting the svg image, so the opportunity to simplify does not arise.
And I just do not know Inkscape well enough to find that option.  It's not one of those in the dropdown on upper right of the window.
I am happy to share the original photo and svg output, attached herewith.

The trace contained in the svg has numerous grayscale traces that are not needed. If going this way, I'd delete all of them except the most accurate path and work from there.

A better method, in my experience, is to bring the jpg image into fusion as a decal or similar, and hand sketch a precise profile for the part in Fusion's sketch mode.. This can be done in Inkscape too, but you're going to Fusion anyway.

You are right, the svg I attached does contain grayscales. there are two rulers plus shadow of the target object. I tried to eliminate the shadows without success using my phone camera.  

The rulers turned out to be handy when I used the same jpeg  to insert  as canvas into fusion 360 when I had trouble getting fusion 360 to properly scale the svg upon insert. But the calibrate function   worked easily and accurately.

I rashly assume that a workflow exists to efficiently and quickly convert a jpg to svg then have it insert to F360 and be scalable, but I have not found it. I must assume I must be stupid.. if it worked as expected then tracing of the image would be unnecessary.  

I'd like to discover the right technique for the future but current task is now almost complete. 

Thanks to those who responded. I continue learning

. 

" I had trouble getting fusion 360 to properly scale the svg upon insert."

That is really an easy fix. 

(1) Simply import the SVG/DXF.

(2) Window Select the entire SVG/DXF imported profile.

(3) Unfix it.

(4) Then use the dimensional tool to specify height, width of the imported SVG or even dimension a single element. Everything will rescale proportionally to that dimension. There is a limit to how much you can up or down scale it with this technique until the sketch profiles break due to inherit SVG precision.

*** Note***: You must have "Scale entire sketch at first dimension" enabled in design preferences for this technique to work. Then you can disable this after the rescale.

IF you are starting from scratch (not scanning or tracing) with a design in Inkscape for Fusion 360, I have found the following tips quite useful: 

https://maakplek.nl/wiki/doku.php?id=from_inkscape_to_fusion_without_scaling_issues&fbclid=IwAR2mOBODHCMLZefSksGKJ6MUnddARg8OJilGrpYtkiOhg7eO8Nt-SHYXSnw

Once I started using those tips - never had scaling issue after that. 

For anything else (scanned, purchased SVGs) - I  use the previous tip once imported in Fusion 360.