(the following questions can be asked by your "opponents")

Why do you want to change a working technology in your company?
if CR is used and works fine, why changing to a new technology?
What are the costs advantages?
What we can't do today and we will do with a DW?

Using a reporting solution does not need datawarehouse, today a lot of
reports can be generated directly from an operationnal system. So if you ask
for a datawarehouse solution, is that because you want to provide more power
and new features to your users, so its a good argument for you.

Providing ad-hoc analysis features is a good point which required a
datawarehouse. And using this datawarehouse for the end users reports is
important to make sure that everyone will see the same cleansed information.
But does your user really need ad-hoc access?
If a user open 1 report by month, too bad. If a user asked you for a new
report every day, you have found the solution.

Crystal report cannot be compared to analysis services and a datawarehouse
solution!
So switching from a simple reporting solution to an ad-hoc query solution
based on OLAP cubes + reports is not allways simple. You'll win only if your
boss need to have answers to questions and if today these answers takes a
long process.
No added value, you'll loose.
Find a guy who need this type of solution in your company (like a HR analyst
or financial manager...) and this person will help you to promote your idea.
No sponsor, no success.

From my experience, if you found a process improoved by a datwarehouse
solution, you win.
In my job, I have reduced the time to create the budget from 2 months to
1week.
I have provided near real time access to information only available only 1
time a day before, and with a higher data quality (in a manufacturing
company).
In another hand, I have projects failure: too complex system not used by the
end user is the first reason. Data not needed by the end user in the
datawarehouse. Bad change management following the project=not used project.

Be prepared for a lot of questions is your better way to win.
Propose a prototype is also a good way to convince you boss, if they can
compare the old and new version of their job, they promote you :-)