By all means, but then again in the trivial case one may be better off turning off the gradebook altogether. Otherwise, there is already enough manual work with the gradebook that the locking and hiding of some items becomes insignificant. At any rate, since activities already allow selecting a gradebook category this issue may be resolved by setting the default of uncategorized gradebook items to locked and hidden or implementing a built-in locked and hidden category for such activities. This may force users to systematically categorize activities but that's just for the best. And to anticipate future wishes the category selection in the activity level may be implemented so as to create the category in the gradebook if it doesn't exist. But then don't we end up simplifying one part by complicating another?
Itamar Tzadok
Повідомлення, що надісла(ла)в Itamar Tzadok
You can lock the quiz's gradebook item and hide it. The locking will prevent the quiz scores from being recorded in the gradebook and the hiding will hide the item from students. If you have many such items alongside some others which you do grade, you can put all the 'practice' items in a designated gradebook category, lock and hide the category, and keep it collapsed in the grader report so that they remain out of the way. 
Use formulas to create Moodle XML of the questions (V column in the example below), copy/paste it to a quiz import file and import. The following is a simple example for single correct answer MC questions with 4 options (for multiple correct answers the formulas are more complex). The correct answer is always the first option and shuffle answers is enabled. The columns IDs are not important and added just for readability. There might be downloadable template(s), perhaps in the exchange site, but this should be fairly easy to construct on your own. Also, there are other import formats you may find preferable over the Moodle XML and you should be able to find info about that in the docs. Hope this helps. 
Example:
L2: question name
M2: question text
G2: Correct answer (always the first; shuffle is enabled)
H2: Distracter
I2: Distracter
J2: Distracter
O2: ="<question type='multichoice'><name><text><![CDATA["&L2&"]]></text></name><questiontext format='html'><text><![CDATA["&M2&"]]></text></questiontext><penalty>0</penalty><hidden>0</hidden><shuffleanswers>1</shuffleanswers><single>true</single>"
P2: ="<answer fraction='100'><text><![CDATA["&G2&"]]></text><feedback><text><![CDATA[]]></text></feedback></answer>"
Q2: ="<answer fraction=''><text><![CDATA["&H2&"]]></text><feedback><text><![CDATA[]]></text></feedback></answer>"
R2: ="<answer fraction=''><text><![CDATA["&I2&"]]></text><feedback><text><![CDATA[]]></text></feedback></answer>"
S2: ="<answer fraction=''><text><![CDATA["&J2&"]]></text><feedback><text><![CDATA[]]></text></feedback></answer>"
T2: </question>
V2: =O2&P2&Q2&R2&S2&T2
The template import txt file:
<?xml version='1.0' encoding='UTF-8'?><quiz>
</quiz>
Example:
L2: question name
M2: question text
G2: Correct answer (always the first; shuffle is enabled)
H2: Distracter
I2: Distracter
J2: Distracter
O2: ="<question type='multichoice'><name><text><![CDATA["&L2&"]]></text></name><questiontext format='html'><text><![CDATA["&M2&"]]></text></questiontext><penalty>0</penalty><hidden>0</hidden><shuffleanswers>1</shuffleanswers><single>true</single>"
P2: ="<answer fraction='100'><text><![CDATA["&G2&"]]></text><feedback><text><![CDATA[]]></text></feedback></answer>"
Q2: ="<answer fraction=''><text><![CDATA["&H2&"]]></text><feedback><text><![CDATA[]]></text></feedback></answer>"
R2: ="<answer fraction=''><text><![CDATA["&I2&"]]></text><feedback><text><![CDATA[]]></text></feedback></answer>"
S2: ="<answer fraction=''><text><![CDATA["&J2&"]]></text><feedback><text><![CDATA[]]></text></feedback></answer>"
T2: </question>
V2: =O2&P2&Q2&R2&S2&T2
The template import txt file:
<?xml version='1.0' encoding='UTF-8'?><quiz>
</quiz>
You may be able to get close to what you're describing above by constructing the multiple choice questions as Cloze questions rather than MC. The Cloze question should look something like:
Who is the sculptor ...
a. {:MULTICHOICE:=X#~V#} Donatello
b. {:MULTICHOICE:=X#~V#} Leonardo
c. {:MULTICHOICE:=X#~V#} Giotti
d. {:MULTICHOICE:=V#~X#} Michelangelo
and will look like the image below. The dropdown allows to select either V or X. Of course the drawback is that this way the student has to select for each option either X or V and nothing will prevent him or her for selecting two V when only one is required either intentionally or by mistake.

Who is the sculptor ...
a. {:MULTICHOICE:=X#~V#} Donatello
b. {:MULTICHOICE:=X#~V#} Leonardo
c. {:MULTICHOICE:=X#~V#} Giotti
d. {:MULTICHOICE:=V#~X#} Michelangelo
and will look like the image below. The dropdown allows to select either V or X. Of course the drawback is that this way the student has to select for each option either X or V and nothing will prevent him or her for selecting two V when only one is required either intentionally or by mistake.
Unless of course elimination is the pedagogical objective of the quiz.