I have a Dissemination Areas boundaries shapefile with has an attribute table full of data needed for lowest quartile analysis and I have a neighborhood shapefile which has lowest income data which also needs to be considered but am not sure how I can combine these shapefiles so I can consider both the lowest income neighborhood data as well as the dissemination area data in my analysis of worst overall dissemination areas. I tried spatial joining but they don't share a similar value.
This depends of course completely on your data.
Let's take into account the following 4 topologies (https://pro.arcgis.com/de/pro-app/tool-reference/data-management/select-by-location-graphical-examples.htm):
Dissemination COMPLETELY_CONTAINS neighborhood
Dissemination INTERSECT neighborhood
Dissemination COMPLETELY_WITHIN neighborhood
Then for the first option in the spatial join window (sorry for the German) the join will work for the cases 2-4. The count column shows how many neigborhoods intersects the Dissemination areas. If there are more you need to decide if you want to have mean, max, min ect. The second option of the spatial join only joins if case 4 is true.
NOTE: The Geometry of the Dissemination areas will not change, only attributes are joined.
I don't think you can spatial join if your geometries do not overlap somewhere. The way I would do it is to convert your boundaries (lines) to polygons, merge them and then you would have your data merged as well. Just check if your boundaries are closed and isolate them before.